232 STROPHOIVIENIA AGASSIZI. 



outer opening the intestine becomes almost square in cross section (Plate 2, 

 fig. 7) and opens with the shell gland into the cloacal chamber. 



The heart is a long tubular organ that near its posterior end falls into 

 two divisions as in a few other species of this genus. The aorta, as it springs 

 from the forward end of the heart, is of large size but as it courses anteriorly it 

 assumes normal proportions, and the route it follows and that of the blood after 

 leaving the head region, are typical in all essential particulars, save that the 

 visceral cavity is of more than usual proportions owing to the absence of the 

 usual amount of connective tissue. 



In the midst of connective tissue and muscle fibres tracing out the dis- 

 tribution of the smaller nerves is an arduous and time consuming task but 

 when these last named elements are free in the visceral cavity they may be fol- 

 lowed with exceptional facility and their study has yielded some interesting 

 results. The brain (Plate 1, fig. 4) not only holds the usual position but gives 

 rise to the customary three pairs of nerves leading to ganglia about the bases 

 of the cirri and in addition originates the lateral, pedal, and labiobuccal con- 

 nectives. Those passing to the cirri are in nowise pecuHar and the same is 

 true for the connectives save that they are more than usually separated as they 

 pass out from the brain, the lateral and pedal laterally and the labiobuccal 

 close to the mid line near the posterior border of the brain. 



The lateral gangUa are of approximately even calibre, showing no especial 

 enlargement where they unite with the connective from the brain. In the case 

 of the ventral cords, on the other hand, such a swelling occurs and marks the 

 point from which the first latero-pedal connective takes its rise. Beyond this 

 point connectives and ventral commissures occur with considerable regularity, 

 the latter being usually of sUghtly larger diameter. In practically every case 

 in the anterior and posterior ends of the body (the middle portion of the body 

 was not sectioned) delicate branches pass from the connectives to the body 

 wall where they disappear from view among the somatic muscles. Other nerves, 

 usually of larger size, originate from the lateral cords and may pass dorsally 

 or ventrally, but in every case they become lost in the body wall without being 

 continuous across the mid line. 



The labiobuccal connectives, lightly resting against the sides of the pharynx, 

 pursue their course to the neighborhood of the radula where they join the labio- 

 buccal ganglia united by the usual heavy commissure passing ventral to the 

 pharynx and dorsal to the radula. Anterior to these gangUa an enlargement 

 occurs in each connective and from them two connectives arise, one situated 



