No. 541] 



THE CANADIAN OYSTER 



39 



extruding its eggs. I also tried Atlantic oyster eggs 

 with Pacific oyster sperms, as well as Atlantic oyster 

 sperms with Pacific oyster eggs, but without success, as 

 one might suppose. I put eggs, embryos and larvae of 

 both species together under the same coverslip for com- 

 parison — those of the small British Columbia oyster 

 looking like giants beside those of the large Prince Ed- 

 ward Island oyster. This is a curious phenomenon 

 which I have several times observed on other species, 

 c //.. the very large eggs of Astarte compared with the 



For the study of segmentation, etc., the Atlantic species 

 is of advantage on account of smaller size and greater 

 transparency. The order of segmentation appears to be 

 the same in both— both subject to variations such that it 

 would require a great number of painstaking observa- 

 tions to decide exactly what is the normal mode in good 

 healthy eggs. I have, on both sides of this continent, 

 spent considerable time in trying to determine the order 

 of segmentation, the cell-lineage, the planes of cleavage, 

 the succession of nuclei, the effect of gravitation, the 

 constant and continuous orientation of successive stages, 

 the origin of the shell-gland and the mode of formation 

 of the shell, etc., but can not discuss such subjects here. 

 I may briefly state, however, that I believe Brooks failed 

 to observe the shell-gland, in his original work, and at 

 one particular stage mistook the relation of the shell 

 valves to the blastopore which made it necessary to re- 

 verse his orientation of the embryo — hence his use of the 

 terms dorsal and ventral are misleading. The polar 

 bodies are dorsal at first— later, if they persist, they may 

 become displaced anteriorly. The blastopore is ventral, 

 the velum anterior, the shell-gland dorsal, the mouth 



I have found conchiferous young of the British Colum- 

 bia oyster retained within the parent's shell until their 

 own minute shells were .138 mm. in length. I believe 



