382 PROCEEDINGS OF THE ACADEMY OF [May, 



left arch of the pair in XI, and sometimes the posterior sperm sac in 

 addition. 



Spermathecse (fig. 6) are nearly always conspicuous even in young 

 worms. They open either very close together or by a common median 

 pore just behind the luirovv l^, and consequently are well forward in 

 the latter somite. They have short, thick, muscular ducts without 

 glands, and ovoid or sometimes nearly spherical ampullse which when 

 fully distended may reach nearly the length of the somite. Wlien 

 fully distended the lining epithelium is thin and flat and the muscular 

 layer thin, but when nearly empty the former becomes thick and 

 folded, often in a spiral or annular fashion, a condition which usually 

 prevails near the entrance to the duct, where the circular muscular 

 layer is much thickened. The spermatozoa are never fashioned into 

 spermatophores, but fill the ampulla in compact masses and bundles. 

 This species is closely related to Monopylephorus ruhronivens Levin- 

 sen, to which Ditlevsen has recently referred Vermiculus pilosus Good- 

 rich. From this species, as elaborately described by Goodrich, M. 

 glaher differs in the entire absence of villous processes on tne cuticle, the 

 greater number of seta?, the form of the nephridia and some minor char- 

 acters of the vascular system, brain, etc. 



Another closely related species is M. fluviatilis (Ferronniere), but 

 if the sperm ducts are correctly figured for the latter the position 

 of the prostate glands is quite different. 



Both Goodrich and Ditlevsen have attached much importance to 

 the form of the nephridia, which they consider to approach the enchy- 

 trseid type. In M. glaher this resemblance is entirely superficial and 

 the arrangement of the tubules is nearly typically tubiciform, their 

 analysis into glandular region, large and small tubule loops being easy. 

 In suitable localities this species is very abundant about the shores 

 of Vineyard Sound and Buzzard's Bay. It prefers regions overlaid by 

 a layer of fine organic mud in places where there is an accumulation of 

 decaying eel grass or other vegetable matter, and especially where the 

 salt water is diluted by springs or streams of fresh water. In such 

 places it occurs in enormous numbers beneath stones or a short distance 

 below the surface, while in nearby spots, where the water is of much 

 o-reater density but the conditions otherwise similar, few or none will 

 be found. Nowhere in this region have these worms been found in 

 greater numbers or of such large size (mostly exceeding 40 mm. in 

 length and 1 mm. in diameter) as along the gravelly and muddy banks 

 of the Wareham river, a small stream emptying into the head of Buz- 

 zard's Bay. Here under stones near high water-mark, at a point where 



