PROaRESS OF MICROSCOPICAL SCIENCE. 281 



The Original Distinction of the Testicle and Ovarii* — This paper 

 is of the utmost importance, as it bears so tliorouglily upon Haeckel's 

 theory. It is by M. Van Beneden, of Liege, and we quote the 

 following translation of part of it from the ' American Naturalist ' 

 of November, 1874 : — 



" Huxley was the first who demonstrated that the entire organi- 

 zation of the zoophytes, meduste, and polypes, hydroids and Siphon- 

 ophores, can be reduced to a sac formed of two adjacent cellular 

 layers, the ectoderm and endoderm (Allman), and who considered 

 this proposition as expressing the general law of structure in the 

 zoophytes. I Although one did not dream at this period of seeking 

 homologies between the vertebrates and lower animals, Huxley took 

 in all the bearings of his discovery. He recognized and formulated 

 in clear and precise language his opinion on the homology which he 

 believed exists between the ectoderm and endoderm of the Coelen- 

 terata, and the two primordial cellular layers of vertebrates. See in 

 what terms he expresses this idea : — ' The peculiarity in the structure 

 of the body-walls of the Hydrozoa, to which I have just referred, 

 possesses a singular interest in its bearings upon the truth that there 

 is a certain similarity between the adult state of the lower animals 

 and the embryonic conditions of higher organizations. 



" ' For it is well known that, in a very early state, the germ, even 

 of the highest animals, is a more or less complete sac, whose thin 

 wall is divisible into two membranes, an inner and an outer ; the 

 latter, turned toward the external world ; the former, in relation 



with the nutritive liquid, the yolk The various organs are 



produced by a process of budding from one, or other, or both of 

 these primary layers of the germ.' 



" He seeks likewise to establish a parallelism, from a histological 

 point of view, between the ectoderm of zoophytes and the external 

 layer of the embryo of vertebrates on one hand, and the endoderm 

 and internal layer on the other. He concludes by saying, 'thus 

 there is a very real and genuine analogy between the adult Hydrozoon 

 and the embryonic vertebrate animal.' All the embryological researches 

 made in late years, in the first phases of the embryonic development 

 of animals of all branches, have tended to confirm, extending it to 

 the whole animal kingdom, the opinion of the illustrious English 

 naturalist. And in the first rank of work done in this direction may, 

 without fear of contradiction, be cited that of Kowalevsky ; in showing 

 the identity of development of Amphioxus and of the Ascidians, he 

 closed with a single stroke the abyss, thought to be impassable, which 

 separates the branch of vertebrates from all the lower organisms. The 

 important publications of the same author on the other types of 

 organization, added to those of Gegenbaur, Haeckel, Eay Lankester, 



* ' De la Distinction originelle du Testicule et de I'Ovaire ; Caracture sexuel 

 des deux Feuilkts primoidiaux de rEmbiyon ; Heimaphrodisme morpholo- 

 gique de tonte Individualite animale ; Essai d'une The'orie de Ja Fe'condation.' 

 Bruxelles, 1874. 8vo, pp. 68. 



t " Observations upon the Anatomy of the Diphydfe and the Unity of Organi- 

 zatiou of the Dipbydte and Siphonophorre." ' Proceedings of Royal Society,' 1849. 



