404 



PROCEEDINGS OF THE ACADEMY OF 



[Sept., 



arteries (fig. D, Lpa), with which, by three short canals, the sinus 

 about the pleuro-pedal gangha is brought into connection. The foot 

 is thus suppHed by the above-mentioned vessels and by the neural 

 arteries surrounding the ventral nerve cords. The fact that so im- 

 portant a portion of the nervous system literally floats in a blood sinus 

 gives an excellent clue to this portion of the system in Haliotis. By 

 referring to fig. C it will be seen that the blood, having once gained the 

 sinus about the pleuro-pedal ganglia, is free to work its way about the 

 intestines, and to some extent the remainder of the viscera. The path 

 is not so unobstructed as one might imagine from the figure, but even 

 though a considerable amount of connective tissue does surround the 

 gut, it is nevertheless penetrated by numerous fairly well defined 

 channels. 



M.-t 



Aid 



Fig. C. — Section passing through front end of cohnnellar muscle and pleuro- 

 pedal ganglia. Aps, anterior pedal sinus; Apn, nerves to front end of 

 foot; Lpa, lateral pedal artery; Mn, mantle nerves; CE, oesophagus; 

 Pal.a, pallial artery; Pl + p, pleuro-pedal ganglia; Ps, pallial sinus; Rr, 

 radula muscle; Sub, Sup, sub- and supra-intestinal nerve. For explana- 

 tion of other letters see plate. 



Following back along the cerebro-pleural and pedal connectives the 

 blood finds its path readily into the head cavity. This surrounds the 

 buccal cavity and lies between its wall and that of the head. In it the 

 cerebral ganglia are situated, together with the salivary and sugar 

 glands. It is somewhat indefinitely bounded, but it may be said that 

 it extends posteriorly beyond the hinder border of the sugar glands. 

 Its wall is of a spongy nature, permitting the blood to ooze out of the 

 head cavity into the visceral cavity. The latter is a true hsemocele, as 

 reported by Woodward for Pleurotomaria. At the left upper and 

 posterior end of the head cavity there arises, by two or three roots, 

 the main pallial artery. Passing along the left side of the neck in the 

 body wall (fig. C, Pal.a), it turns somewhat to the left and enters the 



