Prof. E. Claparede on the Structure of the Annelida. 353 



Reproductive Apparatus. 



The reproductive apparatus of the Annelida has hitherto been 

 very imperfectly known. Numerous works have indeed thrown 

 fresh light upon the educatory organs, known, since Dr. Williams 

 wrote upon them, by the name of segmental organs. But as 

 regards the sexual glands our knowledge has made but little 

 progress for the last thirty or forty years. This memoir will, I 

 hope, make known these organs in a satisfactory manner in a 

 great number of species. M. Ehlers limits himself to saying 

 that the sexual glands may be referred to a single fundamental 

 type — namely, that of a coherent cellular mass, engendered on 

 the inner surface of a part of the wall of the body, or on the 

 dissepiments. This statement is true in many cases. M. Krohn 

 saw the ovules make their appearance as a sort of epithelium on 

 the surface of the dissepiments in Alciope ; and I have myself 

 made perfectly similar observations on Protula Dijsteri. This 

 rule cannot, however, be regarded as general. The sexual glands 

 often present themselves under pei'fectly different conditions. 



The observations of M. de Quatrefages relate chiefly to the 

 Nereida and Eunicea. He has seen the sexual elements make 

 their appearance in these Annelida in a glandular organ extended 

 beneath the abdominal nervous chain. This description is at 

 any rate very inaccurate, as will be seen hereafter on reading 

 the exposition of the singular construction of the sexual glands 

 in various Lycoridea &c. 



The distribution and structure of the sexual glands in the 

 Annelida is subject to numerous variations, which will be illus- 

 trated by a multitude of examples in the course of this memoir. 

 Nevertheless the following form may be regarded as the most 

 generally diffused among the Annelida : — The sexual glands form 

 more or less complex racemes or networks of cords, the axes of 

 which are occupied by sanguiferous branches, which are often 

 contractile. The sexual elements in course of growth form ruffs 

 all round the vascular axes, and become developed at the ex- 

 pense of a layer of nuclei contiguous to the vessel. In the females 

 the ovules are often in immediate contiguity to each other in the 

 ovary ; but sometimes (in Owenia, Delle Chiaje, and some species 

 of Polynoe) each of them is enclosed in a special ovisac. In all 

 cases the ova, when arrived at maturity, detach themselves from 

 the ovary, either immediately, or mediately by the rupture of the 

 ovisac. For the most part the spermatozoids likewise detach them- 

 selves from the testes to float freely in the perivisceral cavity. 



This fundamental form undoubtedly sometimes undergoes 

 important modifications — for example, to produce the singular 

 sexual tissue of the Nereidea or the floating testes of the Dasy^ 



Ann. ^ Mag. N. Hist. Ser. 3. Vol.w. 24 



