ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 851 



layers of the Coelenterata. In other words, we are led to believe 

 that the layers of the gastreea from which the Coelenterata arose 

 were not differentiated into an animal and a vegetative series. The 

 views of the author on this point are carefully elaborated. 



It is pointed out that the distribution of the different kinds of 

 endodermal cells differs in different Hydroid-polyps, but is constant 

 for the species ; in the present case no high degree of differentiation 

 has been attained, and three kinds of cells are found, one with 

 another, in the walls of the stomach. 



In giving an account of the blastostyle the author points out that, 

 if we consider the homologies of the cleft blastostyle, we come to the 

 conclusion that they are the persons which provide us with an inter- 

 mediate stage between the nutrient animal and the medusa ; by sup- 

 posing the oral and aboral walls of the pulsating gastric space to 

 become fused with one another, and the central solid disk to be 

 broken through, we arrive at the structure of a medusa. The peri- 

 pheral portion of the gastric space will become the circular canal, 

 from which arise four radial canals, which lie in transverse axes, and 

 unite at the aboral pole. On their inner and ventral face there bud 

 off the persons which carry the genital products. The importance 

 of the new genus in the discussion of this question is demonstrated. 



After an account of the structure of the medusoid forms, the 

 author passes to the lessons which Eucopella teaches with regard to 

 the doctrine of the germinal layers ; in the first place, it is to be 

 noted that in the differently constituted persons which make up the 

 life-cycle of this form the two germinal layers have to perform very 

 different functions. The nutrient animal possesses in its endoderm 

 all kinds of cells save the chitinous, while in the ectoderm those that 

 are devoted to digestion and excretion are absent ; the mesoderm con- 

 sists, in addition to the indifferent supporting lamella — of muscular, 

 ganglionic, and urticating cells. In the female Medusa we find rela- 

 tions which are essentially different, for the ectoderm has here 

 undertaken a great part of the functions of the endoderm of the 

 trophosome, as might be supposed from the free and ephemeral mode 

 of life ; the endoderm consists of similarly constituted cells, filled 

 with brown pigment, while in the ectoderm there are covering, 

 supporting, and sensory cells, as well as cnidoblasts. In the male 

 medusa the ectoderm also contains the spermatophores with the 

 spermatozoa. 



Attention is drawn to the conclusion that the Coelenterata appear 

 to be distinguished by the fact that in them alone the mesoderm arises 

 at all points of the surface, instead of from one or a few definite cells. 

 In Eucopella we may see the cells, which are about to become ova, 

 pass below the epithelium, and so become mesodermal. It is further 

 to be observed that the umbrellar cavity, which is closed in the 

 young, is formed by the dehiscence of the cells of the central cavity ; 

 the great difference between the higher animals and the Craspedota 

 does not lie in the complete absence of a coelom in the latter, 

 but is due to the primitive method in which their mesoderm is 

 formed. 



