The Structure of the Annelids. 367 



organs known, since Dr. Williams described them, tinder the 

 name of segmentary organs ; but our knowledge of the sexual 

 glands has made little progress for the last thirty or forty 

 years. This memoir will, I hope, make these organs, in a 

 great number of species, sufficiently known." 



M. Claparede then remarks on the very inexact description 

 of M. Quatrefages, and continues : 



11 The distribution and conformation of the sexual glands of 

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

 trated by numerous examples in this memoir. The following 

 may, however, be regarded as the most widely diffused. The 

 sexual glands form more or less complex clusters or interlace- 

 ments of cords, of which the axes are occupied by sanguiferous 

 branches, often contractile. The sexual elements, when grow- 

 ing, form ruffs round the vascular axes, and develop at the 

 expense of a layer of nuclei close to the vessel. With certain 

 vesselless Annelids this form of sexual gland is preserved, but 

 the axis is occupied by a solid cord, instead of a vessel. 

 Among the females, the ovules are often in close juxtaposition 

 in the ovary; sometimes, however (Oivenia, Delia Chiaje, and 

 certain Polynoe), each one is inclosed in a special ovisac. In 

 either case the eggs., on arriving at maturity, detach them- 

 selves from the ovary, either directly or indirectly, through 

 rupture of the ovisac. 'The zoosperms detach themselves from 

 the testicle to float freely in the perivisceral cavity. Doubt- 

 less this fundamental form is sometimes subjected to important 

 modifications, to constitute, for example, the peculiar sexual 

 tissue of the Nereidians, or the floating testicles of the Dasy- 

 branchians, which will be specially described. The egg- 

 formation of the Terebellians and Serpulians is still more 

 divergent, but we always find a cellular tissue, fixed, or com- 

 posed of floating materials, in the midst of which the sexual 

 elements are developed. . . . 



"The sexual glands have long been recognized in many 

 Annelids, but these old observations have been partly forgot- 

 ten. Thus, while Pallas erroneously supposed the eggs of the 

 Aproditians to originate in the liquid of the perivisceral cavity, 

 Gtott, B. Treviranus and Delia Chiaje recognized the true 

 ovaries at the base of the feet of these worms. . . . Even the 

 existence of a sanguiferous vessel in the axis of the sexual 

 glands was not unknown." 



M. Claparede points out the errors of various authors, and 

 adds : — 



" It is indubitable that Annelids exist which are destitute 

 of segmentary organs, or in which they are reduced to simple 

 openings in the back of the body. 



"Nervous System. — It is, without doubt, to M. Quatrefages 



