302 M. E. Claparede on the Theory of the 



1848*, I find the description of the mode in which the ova are 

 formed in the Modiolarice and Cardia, which agrees exactly with 

 that furnished by Leuckart for the Anodons. He also saw that 

 the ova are prolonged into peduncles at the point where they 

 adhere to the ovarian caeca. 



The completion of the " Confirmation " of BischofF was soon 

 furnished by the classical work of Meissner on the anatomy 

 and development of Mermis albicans f, a species of Gordius, 

 which when young inhabits the caterpillars of Hyponomeuta cog- 

 natella, and which afterwards passes into moist earthy where its 

 generative organs acquire their final development and repro- 

 duction takes place. In speaking of the formation of the ova, 

 Meissner incidentally mentions the micropyle. This work is 

 important, inasmuch as it sets forth the homology of the male 

 and female sexual organs, and the analogy between the semen 

 and the ova. The male and female generative organs of Mermis 

 are, in fact, perfectly similar and consist of a very long vessel, so 

 that it is impossible to distinguish the internal generative organs 

 of the male Mermis from those of the female, unless by the 

 microscopic examination of their contents. The upper part of 

 the generative tube or vessel of the male, the part designated 

 by Meissner as the testicle, is filled with round cells, as clear as 

 water, and composed of an extremely delicate enveloping mem- 

 brane, an enclosed liquid, and of a large pale granulated nucleus, 

 containing a nucleolus. These are the male germ- cells {mdnn- 

 liche Keimzellen) as Meissner calls them. The nucleus of these 

 cells in the course of its development exhibits a fine line on its 

 surface, which soon becomes a groove and afterwards a con- 

 striction, until at last the nucleus divides into two. The nucleole 

 does not divide, but remains in one or other of the secondary 

 nuclei [Tochterkern) . The secondary nuclei become larger and 

 divide in their turn, and the nuclei of the third series thus 

 formed follow their example, and so on, until we find germ-cells 

 of the size of y^^ to -^-^ of a line, containing as many as twelve 

 or sixteen nuclei, which all finally attain the size of the primary 

 nucleus. Each of these nuclei is soon seen to acquire a clear 

 border, — this is a membrane formed by a diff'erentiation of the 

 central and peripheric parts of the nucleus. This membrane is 

 constantly removing further and further from the centre, and in 

 this way the secondary nuclei [Tochterkern) are converted into 

 secondary cells [Tdchterzellen) which completely fill the primary 

 cell. The latter then bursts or becomes absorbed, and the 



* Bidrag till Kannedomen om utvecklingen af Mollusca acephala lamel- 

 libranchiata. Aftryck ur Kongl. Vetenskaps-Akademiens Handlingar for 

 ar 1848. 



t Zeitschrift fiir wiss. Zoologie, December 1853. 



