Hyatt.] 114 [March 5, 



transform a Sycon into an animal with a large number of vertical 

 radiating chambers or antimera separated from each other by- 

 vertical mesenteries. Such a form would differ from a taeniolate 

 Hydrozoon or a young Actinozoon in the histology of the lining 

 membrane, since the chambers would be lined with the collared 

 and ciliated cells and the septal edges would have a flat-celled, 

 smooth epithelium. These histological differences, however, are 

 adaptive peculiarities liable to variations between closely allied 

 types like Ascones and Sycones, and also to great changes even 

 in the same animal during the development of the individual. 

 The smaller divisions of the Protocoelomata can be advantage- 

 ously contrasted without unnecessary circumlocution by the use 

 of similar terms. Thus we can term Ascones the Acoelomata in 

 allusion to the pores and the absence of coelomata ; and designate 

 the Sycones as Syringocoelomata, or animals in which the next 

 morphological differentiation takes place by which the diver- 

 ticula of the archenteron extend themselves into the tubes lead- 

 ing to the pores* and lastly the Leucones and Carneospongiae, 

 with their peculiar dendritic extensions of the same cavity, would 

 become morphologically Dendrocoelomata, or branching coelo- 

 mates. 



The researches of Dr. Otto Hamann (Jena. Zeitschr., vol. xiv, 

 1882, p. 500) have shown that ridges or folds of specialized cells 

 exist in the gastric cavity of the Hydrozoa, which can be com- 

 pared closely with the septa of the Actinozoa, especially in the 

 young of Actinia (pi. 20). The histology of the ridges is also 

 sufficiently similar to that described by Wilson, in the septa and 

 filaments of Actinozoa; and there is evidently in the Hydrozoa, as 

 shown by Hamann's drawings, the beginning of a similar differ- 

 entiation to that which exists in the Actinozoa between the diges- 

 tive mesenterial filaments and the epithelium of the septal cham- 

 bers. Prof. Mark has also published (Embryol. Monogr. Mus. 

 Comp. Zool., vol. ix, no. 3) some remarkable figures of the fleshy 

 septa in Edwardsia, which it is interesting to compare with those 

 of Hamann's and Wilson's. The mode of growth of the mesen- 

 teries places an apparent difficulty in the way of the homology 

 of the ampullae with the mesenterial chambers. These last are 

 due to an ingrowth of the endoderm forming the dividing fleshy 

 septa, whereas the ampullae are j^lainly outgrowths or invagina- 



