592 ROBERT SCHARFF. 



Ct. pardalis^ and more so from Ct. monostylos. Its 

 smaller size is the most striking feature, for while Ct. pardalis 

 has from twelve to fourteen segments and a length of 6 — 7 

 mm., Ct. parvulus has only from seven to ten segments and 

 averages about 4 mm. in length. The most important differ- 

 ence, however, lies in the nature of the bristles, which are not 

 pectinated as in Ct. pardalis, but approach in shape one of 

 the two kinds found in Ct. monostylos (fig. 2). 



In the anatomical details, as well as in all the other external 

 characters, Ctenodrilus parvulus agrees very closely with 

 Ct. pardalis. Ct. monostylos has characteristic distinguish- 

 ing features in its peculiar tentacle and in the form of the bristles. 

 In that animal, recently described by Zeppelin,^ two different 

 kinds of bristles have been found, the one straight and needle 

 like, the other slightly bent at the apex. Both occur in the same 

 bundle except in the anterior segments. 



General Characters. — As already mentioned, Ct. par- 

 vulus (fig. 1) agrees in general with Ct. pardalis, and 

 exhibits the same characteristic dark green or violet spots in 

 the skin, which are due to some colouring matter filling up 

 part of the epidermal cells. The colour of the worm itself is of 

 a greenish yellow, which sometimes allows of the internal 

 arrangements being plainly visible in the living animal. On 

 the other hand, very frequently the view is obscured to such an 

 extent by the dark spots in the skin as to render its study very 

 difficult. 



The segmentation of the body is clearly indicated. It is 

 made up of a prostomium, with the head segment bearing 

 the mouth, followed by a number of equal body segments and 

 the tail segment with the anus. 



There are two rows of bristles on each side, and, as in 

 Ct. pardalis, their number in the various metameres is 

 subject to great variation. Sometimes I found only one bristle 

 in the dorsal row and several in the ventral row of the same 



' Max. Graf. Zeppelin, " Ueber den Bau und die Theilungsvorgange des 

 Ctenodrilus monostylos," 'Zeitschrift f. wissenscliaftliche Zoo.logie,' vol. 

 xxxix. 



