98 



ME. E. C. PUNJSTETT ON 



[May 21, 



There are no dorsal commissures. There is a well-marked supra- 

 anal commissure behind the termination of the proboscis-sheath 

 and the dorsal vascular commissure. 



The cerebral organ is large. It begins shortly after the com- 

 mencement of the brain, to the outer side of which it lies. It 

 extends backwards behind the brain, where it lies dorsally and 

 slightly externally to the ventral nerve-cord. It is very large, i. e. 

 about half as large again as the dorsal ganghon, and is richly clothed 

 with gland-cells, especially on the dorsal surface. The opening of 

 the ciliated canal is ventro-lateral, and is situated at the anterior 

 end of the organ. The organ is innervated by a single large nerve 

 which is given off from the hind end of the dorsal ganglion. 



Text-fig. 3. 



dbv. 



oes...//j 



Drepajw^phorus borealis. Section slightly behind the preceding one, showino- 

 the expansions of the rhynchocoelomic diverticula over the cerebral oro-an. 

 (The details of the cerebral oi'gan are omitted.) x 30. 



corff., cerebral organ ; cts., spaces in gelatinous connective-tissue ; dbv., median 

 dorsal blood-vessel ; ext., excretory tubules. 



Other letters as in text-figure 2. 



Portion marked by * enlarged on PL VI. fig. 4. 



There is a well-marked transverse head-furrow on either side, 

 and the two furrows between them surround more than half the 

 circumference of the head. 



