GENUS D1NOPHILUS. 199 



wide ciliated oesophagus, beneath which lies a muscular pro- 

 boscis contained in a special sheath and protrusible through 

 the mouth-opening. Behind the oesophagus is a proventriculus, 

 a small thick-walled ciliated cavity, into which, at its junction 

 with the oesophagus, a pair of salivary glands (sg) pour their 

 secretion. Behind, the proventriculus communicates with a 

 cylindrical stomach, upon which follows the short straight in- 

 testine, terminating in the anus at the posterior end of the 

 body. 



There is no blood vascular system. An excretory system 

 is present, consisting in I), gyrociliatus and D. tceniatus of five 

 pairs of nephridia (ne) which open externally on the sides of 

 the body and terminate in the ccelom-spaces in a funnel con- 

 taining a flame-like bunch of cilia. Whether a direct commu- 

 nication between the lumen of the nephridial tubes and the 

 coelom exists in all cases has not been definitely ascertained, 

 but a similarity of structure to the Platyhelmiuth type of 

 nephridium is shown by the flame-like bunch of cilia and by 

 each nephridium being composed of a series of perforated cells. 

 The reproductive organs are separated in different individu- 

 als ; and in one species, D. gyrociliatus, a marked sexual dimor- 

 phism similar to that occurring in the Rotifera exists, the 

 male being much smaller than the female and possessing only 

 the ciliated ring of the head and the ventral ciliation ; and 

 furthermore the digestive tract and the principal sense- 

 organs are entirely wanting. The reproductive elements (ov) 

 are shed into the ccelom-spaces and find their way to the ex- 

 terior in some species at least by means of the most posterior 

 pair of nephridia, which in the male of D. tceniatus are trans- 

 formed into seminal vesicles and are connected with an intro- 

 mittent organ situated in the posterior segment. 



The nervous system consists of a brain or supracesophageal 

 ganglionic mass which occupies the greater portion of the 

 head segment and from which two nerve-cords pass back- 

 wards in the lateral region of the body, and in D. tceniatus 

 possess ganglionic enlargements equal in number to the pairs 

 of nephridia and the trunk segments and are connected by 

 transverse commissures. In other species, however, these 

 structures have not been observed. Eyes occur imbedded 



