INVERTEBRATA, CRYPTOGAMIA, MICROSCOPY, ETC. 87 



or female, never both; and tlie Opliiurid host often only contains 

 specimens of one sex. 



The chief differences between the development of the two sexes 

 lies in theu- difference in size ; in the male the inner layer is always 

 much smaller than in the female, and contains much smaller cells. 

 In the matured female larva the ectoderm consists of a layer of ciliated 

 cells, which are divided into nine horizontal rows (" segments ") ; 

 the second of these has, however, no cilia, and contains highly 

 refractive corpuscles. The ectodermal cells form elongated six-sided 

 prisms, which have their long axis directed parallel to the long axis 

 of the body. The inner layer is formed of rounded or polygonal 

 cells exactly similar to the above-mentioned ova. The author is not 

 inclined to give to this layer the title of an endoderm. 



Metschnikoff has not, unfortunately, been able to observe the 

 entrance of the fi'ce female larvae into the Ophiurid, nor has he 

 been able to observe the processes of metamorphosis in which the 

 ectodermal cilia disappear. In the more mature males there are only 

 six " segments," and here again the second one is not provided with 

 cilia. 



The writer comes to the conclusion that the Orthonectida are a 

 group of the Metazoa which have become degraded by parasitism, 

 and is not, at present, inclined to regard them as intermediate 

 between the Protozoa and Metazoa, although he allows that a 

 systematic position cannot yet be definitely assigned to them. 



In a subsequent communication,* M. Giard makes some observa- 

 tions on Metschnikoff's paper. He states that though a similar view 

 has often suggested itself to his own mind, he does not feel as yet 

 justified in giving in his adhesion to the hypothesis that the so-called 

 " ovoid form " is the female of {Mac)Intosliia gigas; several differences 

 may indeed be discerned between (^Mac)Intoshia gigas and its supposed 

 female Uliopalura ophiocomoe, ; thus, in the former, the non -ciliated 

 second " segment " is never provided with the highly refractive cor- 

 puscles, while the anterior part of the body is much flattened, and the 

 second segment has on its lower surface a groove of some depth. The 

 writer is strongly opposed to Metschnikoff's view of the musculoid 

 bands of the endoderm being formed by the contours of the tails of the 

 spermatozoa, for they arc visible in young examples, are constant in 

 number, and have always the same oblique disjjosition ; nor can he see 

 why the Russian naturalist refuses the name of endoderm to a layer 

 which arises in just the same way as in so many other animals ; and, 

 as a communication from Professor Louchart has lately informed the 

 author, in Distoma, among otlier Vermes. In conclusion, the author 

 re-asserts liis belief that the gastrula by invagination is the primitive 

 type, and cites in support the observation of Van Benoden on the 

 Digcmida, of Kowalevsky on Actinia, &c., and of Keller on ChaUnula. 



Nervous System of the Plathelminthes. j— Dr. Arnold Lang 

 has an important 2)aper on tlie comparative anatomy and histology 

 of the nervous system of these worms, which was first carefully 



* ' Coiiiptfs Ronihis,' Ixxxix. (1879) p. 1046. 

 t 'Miith. Zool. Stat. Neapel,' i. (1879) p. 459. 



