466 H. J. FLEURE AND MURIEL M. GETTINGS. 



give sketches illustrating the types of cell found in both 

 kidneys (figs. 10 — 12), with the correspondiug cells from 

 Haliotis (figs. 14 and 15) to show the close agreement between 

 these two types j our figures do not agree with those of 

 Perrier and Haller. 



The nephridial gland of Trochus (cf. Perrier's Glande 

 nephridienue of Monotocardia) is composed of a set of 

 branching tubules opening into the kidney cavity, and em- 

 bedded in a tissue rich in blood vessels (Perrier's Glande 

 hematique of Monotocardia). The cells lining the tubules of 

 this gland (fig. 12) are much lower than those of the left 

 kidney. The function of this tissue, as, indeed, the function 

 of the whole left kidney, is quite unknown, but it is, perhaps, 

 important to notice that it occurs along that side of the 

 kidney from which blood channels go to join the efferent 

 ctenidial vein, and to form with it the left auricle. If 

 the nephridial gland of Trochus is really the homologue of 

 the nephridial gland in the Monotocardia, this is an argument 

 in favour of the view of Lankester (5), Pelseneer (7), and the 

 embryologists that the kidney of Monotocardia is equivalent 

 to the left kidney of the Diotocardia. Perrier, Woodward 

 (13), and one of ourselves have urged the opposite view on 

 other grounds which cannot be altogether set aside, and the 

 question must be further discussed after more comparative 

 and embryological research, some of which is now being 

 undertaken. 



Circulation. — In its main features, the circulatory system 

 of the species of Trochus considered agrees with that 

 described by one of us for Haliotis (3). Blood leaves the 

 ventricle by the aorta, the communication being guarded by 

 a simple valvular Hap. The aorta bifurcates soon after leaving 

 the heart, and one branch goes to the visceral hump while 

 the other runs forward and ensheathes the radular sac. This 

 is as in Haliotis, but here the blood channel is practically 

 embedded in the side of the shell muscle for some distance. 

 Still surrounding the radular sac it reaches the liead where 

 a great deal of its blood seems to be directed into spaces 



