88 



however, neither numerous nor detailed enough to allow 

 of a really definite statement being made. On the other 

 hand, the intimate relation between the nephridial gland 

 and the vascular system implies some function connected 

 with the composition of the blood. Perrier discusses two 

 theories, the first that it may be an organ for reserve 

 matter, the second that it is concerned in the formation of 

 blood. The author of this memoir is inclined to believe 

 that the gland is a lymph organ with some additional 

 function : further work is being carried out on the 

 subject. 



The morphological value of this gland is another 

 point of considerable interest, particularly in connection 

 with the attempts made to discover a homologue in the 

 Monotocardia of the second renal organ of the Dioto- 

 cardia, or to determine which renal organ, if any, has gone 

 from the Monotocardia. Originally it was supposed that 

 the renal organ present in the whelk represented the right 

 nephridium of the Diotocardia. Perrier took this view, 

 and starting from the fact that in Patella both organs are 

 present and both are situated to the right of the peri- 

 cardium, he pointed out the resemblance in position of 

 the nephridial gland and renal organ in such forms as 

 Buccinum. His theory, in short, was that the two renal 

 cavities of the lower gastropods had fused, and the left 

 renal organ had passed to the right of the pericardium. 

 Then the right organ had kept its true primary function 

 of excretion, whilst the left became the nephridial gland 

 by development in its walls of tissue with a new function. 

 As further proof of this view, the intermediate forms — 

 Haliotis, Turbo, and Trochus — are brought forward, in 

 which, whilst both renal organs are still present, the left 

 has almost lost its function of excretion. 



Against this we have the fact that the renal aperture 



