602 W. S. NICKERSON, 



more than a third of a millimeter. Posteriorly this tubule is con- 

 tinued into a minute very thin walled vessel similar to the excretory 

 tubules usually seen in sections of trematodes. I have. been able to 

 follow its course but a short distance. Anteriorly the tubule becomes 

 thin walled but larger in diameter and extends forward and upward 

 into the dorsal median lobe of the oral disk nearly to the tip. Here 

 it turns sharply upon itself and extends backward diminished in size 

 as one of the longitudinal excretory vessels which lead backward to 

 the excretory vesicle. It may safely be assumed that so highly 

 specialized a portion of the systera as I have described is of functional 

 iinportance though in what way is at present open only to con- 

 jecture. No such modification of the excretory System has been re- 

 ported of other Aspidobothrids nor so far as I know of other trem- 

 atodes. 



There appears to be a dffference between the two species of 

 Cotylogaster also in the position of the excretory pore. In C. michae- 

 lis it is according to Monticelli at the summit of the dorsal conc ; 

 in C. occidentalis I find it at the base of the cone. The surface 

 appearance of the latter form strongly suggests an aperture at the 

 apex of the cone (Fig. 5) tho' sections show that the aperture is really 

 elsewhere. A comparison of Monticelli's fig. 1, tab. 22 with my 

 Fig. 7 leads me to suspect however that the diti'erence in the position 

 of the aperture in the two forms is really not so great as appears 

 from the descriptions. It appears very questionable whether the dorsal 

 cone "conischen oder cylindrischen Zapfen" mentioned by Jägerskiöld 

 ('99, p. 202 — 203) as occurring in Macraspis can be considered homo- 

 logous with that in ( ^otylogaster since Jägerskiöld's fig. 5, p. 202 

 shows that not only the caudal foramen but also the posterior 

 end of the intestine and the rudimentary sexual organs are con- 

 tained in it. 



No satisfactory description of the nervous System of G. occiden- 

 talis can be given as the brain and nerve trunks are very obscure 

 in the sections and so not favorable for Observation. The brain cor- 

 responds in position with that of C. michaeUs lying above and at the 

 sides of the prepharynx just back of the oral disk and ventral to the 

 thick-walled excretory tubules previously described. The nerves lead- 

 ing from it I have not followed. The study of my sections has given 

 however some interesting facts concerning the peripheral nervous 

 System as represented by the marginal sense organs of the ventral 

 sucker. These organs have been reported as occurring in all the 



