36 ON A XEW SPECIES OF ENTEROPNEUSTA, 



vessels. Further, the "keel" and "body" of the proboscis skeleton 

 are at this point quite distinct from each other and separated by 

 the narrow ventral band of "chondroid tissue," and there is 

 certainly no median prolongation anteriorly from the point of 

 fusion of the "body" and "keel" of the proboscis skeleton which 

 takes place just behind the connecting vessel, and which could be 

 mistaken for the vessel in question. 



We may then take it as characteristic of Pt. australiensis, at 

 least, that the efferent proboscis vessels are united by a connect- 

 ing vessel passing in the "chondroid tissue" between the "body" 

 and "keel" of the prol^oscis skeleton. 



Further, in this species the capillary net of the proboscis comes 

 directl}' into connection with the efferent prol)Oscis vessels in 

 the proboscis neck, and indeed anteriorly to the connecting vessel. 

 In sections through the proboscis neck, in the region of the 

 ventral blind sac, vessels are found in the here commencing 

 "chondroid tissue" which, as Spengel has shown, is simply the 

 thickened limiting membrane of this region into which cellular 

 strands derived mainly from the proboscis pockets have penetrated. 

 Some of these vessels enter the efferent proboscis vessels (fig. 9\ 

 and they thus serve to place the capillary net of the proboscis 

 directly in connection with the efferent proboscis vessels, while 

 the dorsal and ventral efferent skin vessels, since they return the 

 blood first to the glomerulus, do so indirectly. 



Vessels of Collar : The efferent proboscis vessels are continued 

 into the collar, and are related there essentially as in the 

 described species of Ptyclwdera. They appear on their entrance 

 into the collar as clefts in the limiting membrane on either side 

 of the proboscis skeleton, and have at first a longitudinal direc- 

 tion. Very soon they diverge outwards in a fold of the limiting 

 membrane and finally pass downwards round the mouth cavity in 

 a fold of the limiting membrane of the inner wall of the collar — 

 the circular vessel fold. Their dorsal portions are formed of 

 single vessels (fig. 16, cvc.) which ventro-laterally give rise to two 

 capillary nets (fig. 17, cvc'.') which unite in the mid- ventral line of 

 the anterior part of the collar to form the longitudinal ventral 



