supporting lamella

HISTOLOGY AND DEVELOPMENT OF MYRIOTHELA PHRYGIA. 517
space in close communication with all parts of the organism,
and containing not only the results of the solution of the food,
but also material discharged from the lining cells of one region,
and destined for the nutrition of other parts of the organism.
It is as an example of this class that I wish to consider
Myriothela.
2. By the development of a system of spaces or a common
space round the gut, into which the results of digestion can be
discharged, and from which the tissues can directly derive their
nutriment. Such a space would be the hsemocoel of morphologists.
The physiological significance of the coelom is still, I
think, very much under judgment.
3. By the aid of a closed vascular system. The true relations
of hsemoccel and coelome to one another and the relations
of both to the vascular system of Annelids, which appears to
be initially respiratory ; and to the vascular system of Arthropods,
which is in ita first inception a mechanism for the circulation
of the fluids of the circum-enteric space, are questions
which do not concern us here, but the interrelation of
cases 1 and 2 demands brief notice.
It is necessary at the outset to distinguish clearly between
the digestive functions of the enteric space, and the part it may
play in the distribution of the nutritive material. The researches
of Miss Greenwood on the digestive process in Hydra
justify the conclusion that in that animal the enteric space is
used mainly, if not solely, for digestion. The endoderm-cells
forming its walls absorb and largely store the products of
digestion. There our exact knowledge ends, but the uniform
character of the endoderm throughout the entire animal, the
fact that its cells everywhere, even in the tentacles, absorb and
store nutriment, renders it probable that in the physiology of
Hydra the discharge of elaborated nutritive material into the
enteric space to form a common nutritive fluid akin to the
blood of higher animals plays little part. But in the higher
Coelenterates, in the colonial forms, in Medusae, and in Ctenophora
especially, we have no reason to doubt that such a fluid
does exist, and that it forms the metabolic link between the