374 W. BLAXLAND BENHAM. 



in a line with the lateral chsetae (fig. 3). On dissection there 

 appears to be an accessory gland in front and one behind the 

 point of entrance of the duct into the body-wall, similar to 

 that in many Perichaeta and others; but in reality, as sections 

 show, these two ovoid structures are due to the constriction, 

 by Septum vii/viii, of a single sac, with thick muscular walls, 

 which opens externally in the intersegmental groove (figs. 5, 

 13, cop. sac). This sac is lined by a columnar glandular epi- 

 thelium, the nuclei of the cells being at their inner ends (fig. 

 14) similar to that of the spermatheca itself. The sperma- 

 thecal duct perforates the dorsal wall of this sac at about its 

 central point, where it is nipped by the septum, and owing to 

 its cubical epithelium can readily be traced ; the wall of the 

 duct is very thick, being provided with a circular coat of 

 muscles (fig. 15). It appears to me that possibly this sac is 

 a copulatory sac in the true sense of the word, and that the 

 muscular duct of the atrium is to some slight extent eversible, 

 and is received into the copulatory sac. 



Amongst the other species, in which the genital organs liave 

 been described, an arrangement at all comparable to this occurs 

 only in M. Deshayesi. All recent authors agree that Perrier's 

 interpretation of the organs lying in Somite vii as " prostates" 

 connected with an anterior pair of testes is erroneous. Horst 

 regarded these pyramidal glandular organs as " spermathecse," 

 the ducts of which unite to form a short common duct, re- 

 ceiving a more delicate " vas deferens ^^ (Perrier). But Bed- 

 dard has conjectured, rightly as it appears to me, that these 

 glands are comparable to such accessories of the spermatheca 

 as are usual amongst the Perichsetidse. 



Perrier's fig. 79, pi. iv, represents a section through one of 

 the pyramidal organs of Somite vii, which shows its glandular 

 character, but an absence of muscle in its wall. In the present 

 species the glandular lining is relatively thin, the muscular 

 coat being very greatly developed. But in M. indicus no 

 ducts such as Perrier figures exist. I would suggest that the wide 

 bilobed sac in my worm corresponds to these pyramidal organs. 

 In M. Deshayesi a greater differentiation has occurred, the 



