36 
ON A NEW 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 proboscis skeleton. 
Further, in this species the capillary net of the proboscis comes 
directly into connection with the efferent proboscis 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 Ptychodera. 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 1 .) which unite in the mid-ventral line of 
the anterior part of the collar to form the longitudinal ventral 
