The Sexual Conditions of Myzostoma glabrum (F. S. Leiickart). 299 



aspect of the body'. On tlie neural side the development of sper- 

 inatozoa has progressed to such an extent — even in the youugest 

 hermaphrodite — that ali trace of the originai peritoneal epithelium, 

 as such, is lost. It has been almost, if not entirely, converted either 

 into spermatozoa, or into cells of some of the intermediate stages 

 of such formation. 



The enormous development of the setal sacs, with their attached 

 muscles and glands, etc., has also helped to destroy the simple character 

 of the body-cavity on the neural aspect of the alimentary canal. But, 

 on the other band, it is possible in many sections to make out a re- 

 gulär epithelial lining of the body-cavity above or ha^mal to the 

 alimentary diverticula. In such sections as those figured in figs. 1, 

 2, and 4 the regulär skin-epithelium is followed by the usuai connec- 

 tive tissue and muscular sub-dermal layers, and these are bounded 

 internally by the regulär peritoneal epithelium already mentioned. 

 This can he traced in favourable sections along the curve of the body, 

 as far as the lateral margins of the under surface (figs. 5, 13). 



Here and there a rather large egg-cell, projecting from the 

 epithelium but forming one of its elements, may be noticed. In a 

 series of sections ofindividuals of different sizes, such as those of 

 tab. 2, it is not difficult to trace these undoubted egg-cells through ali 

 stages, from the youngest ones, hardly dififering from the cells ad- 

 jacent to them in the epithelium (figs. 2 and 7), to others, which, 

 breaking loose from the latter, are thiis set free to undergo their further 

 development in the body-cavity itself (fig. 5) — a common occurrence 

 among the Polychseta. 



The appearances seen under the microscope support the conclusion, 

 that in Mxjzostoma nearly the whole epithelial lining of the body- 

 cavity is concerned in the production of sexual elements. In other 

 words, this epithelium is a generative organ (Keimdrüse.) 



In the smallest males examined the development of the sexual 

 Organs had proceeded at a much greater pace than in the hermaphro- 

 dites or disc-forms. Traces of the body-cavity were here difficult to 

 detect, owing to the fact, that among the males much smaller indi- 

 viduals, than among the hermaphrodites, shewed the conversion of 

 the coelomic epithelium at various points of the hsemal aspect into 

 sperm-mother-cells, or into stili further stages of developing sperma- 

 tozoa (figs. 11 and 12). 



1 Compare figs. 1 — 4, 6, and 7. 



