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 haemocoel of morpho- 

 logists. The physiological significance of the ccelom is still, I 

 think, very much under judgment. 



3. By the aid of a closed vascular system. The true rela- 

 tions of hsemocoel 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 Arthro- 

 pods, which is in its first inception a mechanism for the cir- 

 culation of the fluids of the circum-enteric space, are ques- 

 tions 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 re- 

 searches 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 Medusse, and in Cteno- 

 phora especially, we have no reason to doubt that such a fluid 

 does exist, and that it forms the metabolic link between the 



