COE : NEMEETEANS OF WEST AND NORTHWEST COASTS. 237 



observed is 10, and this number occurs regularly in two species, 

 while a third form has either 10 or 11, and a fourth 10, 11 or 12. 

 One species has 12 or 13, two others 14, one 14 to 16, one 15, one 

 17, and the number in a single species varies from 17 to 20. These 

 numbers accord well with those of the known species from other 

 parts of the world. 



Gerehral sense organs. — In regard to the relative position of the 

 cerebral sense organs with regard to the brain, by far the greater 

 number, or 13 out of the 19 species in which this relation is known, 

 have the cerebral sense organs situated anterior to the brain. In 

 several of these, this organ is small and situated well in front of the 

 brain, while in others it is nearly as large as one of the ganglia, and 

 lies close against the anterior border of the brain. In the other t) 

 species the sense organs are of very large size and are situated in the 

 angle between dorsal and ventral ganglia, in some forms projecting 

 well in front of the ganglia, and in others extending some little dis- 

 tance posterior to the brain. In all cases, however, the canal which 

 communicates with the exterior passes anteriorly, and usually opens 

 to the ventro-lateral surface of the head a short distance in front of 

 the brain. In some of the species where the cerebral sense organs 

 lie far in front of the brain, the canal opens to the surface but a very 

 short distance behind the tip of the snout. 



Other peculiarities. — Among the other anatomical peculiarities 

 in which certain of these species differ from most other described 

 forms of the genus, the presence of a highly developed esophageal 

 caecum, extending backward beneath the esophagus proper and 

 stomach and ending blindly posteriorly in three species {A. occi- 

 dentalism A. r^ibellus, and A. himacnlatus)., has as yet been observed 

 in but two other species of the genus. ^ The females of two 

 other species are conspicuous Avhen sexually mature because of 

 their bright green ova; at least one species {A. cruentatus) has 

 deep red blood corpuscles, and another [A. flavescens) has yellow 

 proboscis sheath corpuscles. One form {A. punctatuhis) is oval, 

 tlattened, and probably free-swimming; two (^4. imparispinosKS 

 and A. formidabilis) have a large numlier of efferent nephridial 

 ducts, and in one species (^4. drepanophoroides) the intestinal 



1^. marinoratus from Europe (Joubin, '90, p. 564) and A. arcticus from 

 Davis Strait (Pumiett, : 01, p. 94). 



