Reproductive Biology and Embryology of the ... - Seaturtle.org

More documents

Recommendations

Info

39B REPROOUCTIVE BIOLOGY ANO EMBRYOLOGY OF CROCOOILIAN9 evident and may be invaginating. The optic and otic vesicles are also obvious, but the brain is not yet regionalized. The optic pIacodes and vesicles are more obvious than the otic. Flexures and Rotation. The embryo lies at right angles to the yolk surface, that is, body torsion has not yet commenced. Blastopore and Primitive Streak. Obvious. Gut. The gut is incomplete caudally and open ventrally along its entire length. Somitomeres. Three pairs of cranial somitomeres are visible anterior to the otic vesicle. Notochord. The notochord is evident. Stage 2 [Fig. 1 S) Blastoderm. The dorsal surface of the blastoderm is attached to the overlying shell membrane, and the embryo remains so tethered throughout subsequent development. Blood vessels are now visible; one pair emerges from the embryo at the caudal level of the heart, whereas another (larger) pair runs down the lateral wall of the embryo to emerge at approximately the level of the 20th somite. Somites. 21-25 pairs (decreasing markedly in size caudally). Delineation of the Embryo. Dorsally the embryo is almost completely delineated except for a very small circular area at the extreme caudal tip. Ventrally the caudal and caudo-Iateral boundaries of the body wall have formed. Branchial Arches. visible. The 1st and 2nd arches and the 1st branchial cleft are Heart. An extra vertical loop has developed making a total of three loops. The heart lies in the midline of the embryo. Sensory Placodes, Pits, etc. The lens placode and optic cup are defined, and the otic pit is distinctly patent. Brain. Hindbrain discernible as a clear transparent region. Flexures and Rotation. The cranial end of the embryo is flexed at approximately the level of the heart with the head lying at approximately 45° to the plane of the body. No body torsion has occurred. Stage 3 [Fig. 1 S) Somites. 26-30 pairs. Delineation of the Embryo. Complete. Branchial Arches. Three branchial arches, the 1st branchial cleft, the 2nd branchial groove, and the branchial sinus are all present. Tail. Bud present, but lacks somites. Brain. Forebrain, midbrain, and hindbrain are now discernible, the latter appearing distinctly transparent. Sensory Placodes, Pits, etc. The optic cup has an elongated horseshoe BTAGEB OF EMBRYONIC OEVELOPMENT [AFTER EGG LAYING) 399 shape, which extends below the lens vesicle onto the roof of the primitive oronasal cavity. Blastopore and Primitive Streak. Not visible. Extra-embryonic Membranes. The amnion is attached ventrally to the lateral body walls, cranially to the borders of the pericardium about the level of the 7th to 8th somite and caudally to the cranial margin of the fold of tail bud. Flexures and Rotation. Head at approximately right angles to the body. No body torsion. Stage 4 [Fig. 1 S) Somiles. 31-35 pairs. The first is beginning to disappear. Tail. Distinct, straight, and contains 3-5 somites in its base; the tip is unsegmented. Flexures and Rotation. Body torsion has commenced. The cranial half of the embryo is rotated so that its right surface is in contact with the shell membrane and its left is parallel to the underlying yolk. The caudal half of the embryo is not rotated and lies at right angles to the shell and yolk. Heart. Displaced to the left side of the embryo and large. Allantois. Small elevation is just visible immediately caudal to the craniallimit of the ventral tail fold, at approximately somite 27. Branchial Arches. Three branchial arches, the 1st branchial cleft, the 2nd and 3rd branchial grooves, and the branchial sinus are present. The cranial nerves to branchial arches 1-3 are discernible using oblique or transmitted illumination. Stage 5 [Fig. 1 gJ Somites. 36-40 pairs. Only traces of the first somite can be detected, although it is included in this count. Tail. The tail tip bends ventrally at right angles to the body of the embryo; 6-10 somites in its base, tip unsegmented. Flexures and Rotation. Body torsion is complete except for the tail. The head is further flexed with the roof of the brain at approximately 25° to the plane of the body. Allantois. The allantoic bud is distinctly swollen, smaller in height than the tail. Sensory Placodes, Pits, etc. The otic pit lies dorsal to the junction of the 2nd and 3rd branchial arches, and its external opening is closing. Stage S [Figs. 1 S. 1 g. and 23J Sensory Placodes, Pits, etc. Nasal placodes present. Otic pit closed. Limbs. Hindlimb buds are just visible on each side, the right hindlimb ~ bud being marginally advanced over the left, but no forelimb buds are present (Fig. 23).
400 REPRODUCTIVE BIOLOGY AND EMBRYOLOGY OF CROCODILIANS Flexures and Rotation. Body torsion complete. The roof of the brain is at approximately 45° to the plane of the body, whereas the floor of the brain is horizontal and parallel to the plane of the body. Brain. The olfactory bulbs, forebrain, and midbrain are distinct. Four to six neuromeres are discernible in the transparent hind brain area. Tail. The tip is starting to curl but is unsegmented; somites are only present in the proximal region of the vertically oriented tail. Allantois. The allantoic bud is stilI smaller in height than the tail. Gut. The foregut and hindgut are formed, but the midgut is incomplete ventrally. Extra-embryonic Membranes. Many blood vessels in the vitelline and yolk sac membranes; major ones emerge at the level of the 18th somite and other smaller ones at the 6th and 11th somite levels. Stage 7 [Figs. 19, 23, and 27AJ Limbs. Distinct hindlimb bud; forelimb bud just visible as a sinusoidal elevation. The forelimb bud extends over approximately somites 12-15; the smaller hindlimb bud extends over somites 26-28. Differences in size between forelimb and hindlimb buds are more marked in C. johnstoni. Sensory Placodes, Pits, etc. Nasal placode begins to invaginate. Brain. Midbrain bulge evident. Tail. Tail tip, curled at approximately 90° to the remainder of the tail, and contains somites. Flexures and Rotation. At the level of the heart, the cranial region is bent at approximately 90° to the body. The neck region is also flexed, so that the roof of the brain lies at approximately 60° to the body plane and the floor of the brain at 45°. This dichotomy in angulation accentuates the midbrain bulge. Branchial Arches. Three branchial arches, the first branchial cleft and groove, the second and third branchial grooves, and the branchial sinus are present (Fig. 27A). STAGES OF EMBRYONIC DEVELOPMENT (AFTER EGG LAYING) Tail. The tail tip is coiled through two 90° turns and flexion of the tail base has commenced. Twelve to eighteen somite pairs are present throughout the tail. Stage 9 [Figs. 19, 23, 27C and OJ Branchial Arches. Four branchial arches, the 1st and 3rd branchial clefts and grooves, the 2nd and 4th branchial grooves, and the branchial sinus are visible (Figs. 27C and D). Branchial clefts are present only in the dorsal halves of the junctions between the 1st-2nd and 3rd-4th arches, the intervening ventral tissue is continuous and forms the branchial grooves. Facial Processes. The maxillary process is distinct and extends forward to the midpoint of the eye. There are elevated rims of tissue around the nasal pits. A remnant of the ingrowth of Rathke's pouch is visible in the roof of the primitive oronasal cavity. Eye. The optic cup and central lens anlage are large and round but unpigmented. Limbs. There is a distinct apical ectodermal ridge on the hindlimb bud, but not on the forelimb bud. The hindlimb bud extends out farther from the body than the forelimb bud (Fig. 23). Tail. The tail tip is curled through three 90° turns, and the tail base is distinctly flexed from the lower lumbar region; the tail contains approximately 20 somites. Allantois. The large allantois is fused to both the amnion and chorion. The chorioallantois extends around approximately one-half of the breadth of the eggshell. Heart. The distinct atria, ventricles, and the lung primordia are visible through the transparent pericardial sac. Gut and Abdominal Organs. The midgut and body walls are open ventrally from the caudal limit of the pericardial sac to two-thirds the way down the body. The developing mesonephros and liver are just visible through the lateral body walls. 401 Stage B [Figs. 19, 23, and 27BJ Stage 10 [Figs. 19, 23, 27E, 34A and BJ Allantois. Now a large ballooning sac, longer than the tail; it contains blood vessels, but is not yet fused with either the amnion or the chorion. External Genitalia. A small elevated genital tubercle is present. Sensory Placodes, Pits, etc. Nasal pits are present on each side of the head external to the swellings of the olfactory bulbs; Rathke's pouch is invaginating in the middle of the roof of the primitive oronasal cavity to approXimate the infundibulum (Fig. 27B). Limbs. Forelimb and hindlimb buds both distinct and extending over somites 11-16 and 27-32, respectively (Fig. 23). The apical ectodermal ridge is developing on the hindlimb bud. Eye. Pigment in the iris makes the eye appear light black except for the central opaque lens. The right eye is usually pigmented earlier and more heavily than the left eye. Branchial Arches. Five branchial arches, grooves, and the branchial sinus are present. The first cleft lies dorsally, ventral to the otocyst. The third branchial cleft (between arches 3 and 4) is closing over. Branchial arches 1 and 2 are merged together in their ventral halves, and arch 2 has started to overgrow arch 3 (Fig. 27£). Branchial arches 4 and 5 are very small. Viewed from the frontal aspect, the horseshoe-shaped 1st branchial arch is distinctly lobulated in the midline.
Page 1 and 2: 32B EMBRYOLOGY OF MARINE TURTLEB be
Page 3 and 4: 332 REPRODUCTIVE BIOLOGY AND EMBRYO
Page 5 and 6: 138 REPRODUCTIVE BIOLOGY AND EMB
Page 9 and 10: TABLE III Comparative Data on the N
Page 13 and 14: 3152 REPROOUCTIVE BIOLOGY AND EMBRY
Page 15 and 16: 356 I REPRODUCTIVE BIOLOGY AND EMBR
Page 19 and 20: 1 microorganisms in the pores of th
Page 21 and 22: 368 REPROOUCTIVE BIOLOGY ANO EMBRYO
Page 25 and 26: 37B REPROOUCTIVE BIOLOGY ANO EMBRYO
Page 29 and 30: .y A c D r ~•• _.'-';;~~;l'.:!"
Page 31 and 32: 3BB REPRODUCTIVE BIOLOGY AND EMBRYO
Page 35: Stage 2 3 TABLE VI Concordance for
Page 41 and 42: STAGES OF EMBRYONIC DEVELOPMENT [AF
Page 43 and 44: STAGES OF EMBRYONIC OEVELOPMENT (AF
Page 47 and 48: 420 REPROOUCTIVE SIOLOGY ANO EMSRYO
Page 51 and 52: 42B REPRODUCTIVE BIOLOGY AND EMBRYO
Page 55 and 56: 1436 REPROOUCTIVE BIOLOGY ANO EMBRY
Page 61 and 62: Fig. 36. Alligator mississippiensis
Page 63 and 64: TABLE VIII A Systematic Catalogue o
Page 73 and 74: ~ 472 REPRODUCTIVE BIOLOGY AND EMBR
Page 77 and 78: •••••••••••
Page 79 and 80: 494 REPRODUCTIVE BIOLOGY ANO EMBRYO
Page 81 and 82: • .' 4BB REPRODUCTIVE BIOLOGY ANO

Reproductive Biology and Embryology of the ... - Seaturtle.org

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?