ON OTENODRILUS PARVULUS. 595 



interior of the cell. Prof. Ray Lankester^ makes mention of 

 '^ clear cells or vesicles^' as occurring in the skin of Chseto- 

 gaster limnsei, which appear to be identical structures. He 

 tells us fui'ther that the clear vesicles in the integument of 

 many Planarian worms likewise belong to the same order of 

 structures. 



Projecting from the skin we have a certain number of 

 bristle-bundles in every segment, viz. one pair in eacii. I have 

 already called attention to the fact that the quantity of 

 bristles in each bundles is not the same, but varies to a con- 

 siderable extent. A characteristic structure of the Oligo- 

 chsetes, the small involutions from the skin in which the 

 bristles take their origin, is not present here. 



According to Zeppelin, Ctenodrilus monostylos has 

 never less than two bristles in a bundle, while in parvulus I 

 frequently found only one. The shape of the bristle in 

 Ctenodrilus parvulus in distinction to the closely-related 

 Ct. pardalis is that of a spear, the apical part being slightly 

 bent (fig. 2). In the latter species the bristles are pectinated, 

 and in Ct. monostylos there are two different kinds, one of 

 them being long and slender, and the other somewhat resem- 

 bling the one I just described as occurring in Ct. parvulus. 

 Another point of diflference in respect to the bristles of Ct. 

 monostylos is that they project much further from the skin 

 than in Ct. parvulus. 



The Muscles. — Beneath the epidermis we find one very thin 

 muscular layer. There is no perceptible division into a trans- 

 verse and longitudinal part, the layer consisting merely of the 

 primitive longitudinal fibres, which stretch without intermission 

 from head to tail. The few bristles in each bundle are moved 

 by some fibres attached to the general body wall. 



A powerful muscle inserted at the front part of the oeso- 

 phagus causes the protrusion of the lower lip. No special 

 structure can be assigned to the muscular fibre, and, as Zeppelin 

 has pointed out, Ctenodrilus shows great resemblance to the 



^ E. R. Lankester, " A Contribution to the Knowledge of the Lower Anne- 

 lids," ' Trans, of the Linneau Soc.,' vol. xxvi, p. G34. 



