598 EGBERT SCHARFF. 



alimentary canal. It begins here with a wide mouthy its dia- 

 meter decreasing rapidly as it reaches the first segment. The 

 above-mentioned enigmatic organ takes up a central position 

 in the vessel. It, too, attenuates towards the anterior part of 

 the animal and disappears in the head segment. A little more 

 light has quite recently been thrown on the function of a 

 similar hitherto problematical structure by Horst.^ He looks 

 upon it as a gland in connection with a blood-sinus of the ali- 

 mentary canal, the latter being a continuation of the short 

 dorsal vessel. The blood circulating in this sinus is supposed 

 to pass through the glandular organ into the dorsal vessel. As 

 there does not appear to be a sinus in the wall of the alimentary 

 canal of Ctenodrilus we may regard the so-called enigmatic 

 organ as a remnant from some more ancient type, where the 

 organ was of more use in connection with the blood system, 

 and that it has in time undergone retrograde development. 



Segmentation and Segmental Organs. — The outer 

 segmentation corresponds to the inner as in other Chsetopods. 

 This, however, is not the case throughout, and the alimen- 

 tary canal especially shows numerous constrictions quite 

 independent of those of the body. There are from seven 

 to ten segments in Ctenodrilus parvulus, one of the dis- 

 tinctions between it and the closely related Ct. pardalis and 

 monostylos. 



The dissepiments are loose and easily moved forward and 

 backward with the alimentary canal. Between the septa are 

 seen a number of small nucleated cells, which float about the 

 body cavity. Zeppelin is of the opinion that they serve as 

 stores for nutritive material in those individuals which are 

 still unable to provide food for themselves. As these cells 

 appear to be more numerous in specimens that are just under- 

 going division, this view is probably the correct one. 



The small segmental organs are not always clearly discernible. 

 In no case are they distinct enough to admit of their true 

 structure or parts being well recognised. LikeCt. pardalis 



' Horst, " Ueber ein ratliselhaftes Organ bei den Ciiloraemiden," 'Zoologi- 

 scher, Anzeiger,' Jauuar, 1S85. 



