152 Canadian Record of Science. 



sexual maturity is dependent on the temperature of the 

 water; for the deeper the water, the more slowly it be- 

 comes heated up. 



The fact that by the end of August in a cool summer 

 the spawning was over seems to show that the oyster 

 could be fished without damage to the spawn in Sep- 

 tember, and that the close season is unnecessarily long. 



I was not able to secure enough material for a 

 thorough study of the development owing chiefly to the 

 absence of proper facilities for rearing the larvae at the 

 station, but some of the facts gleaned mav be of in- 

 terest. The egg when shed out is pear-shaped — when 

 fertilized it becomes round and separates off two polar 

 globules. These globules are by many eggs — notably 

 those of the sea-urchin — separated out before fertiliza- 

 tion and as concidently with their separation the 

 nucleus of the egg loses its distinct membrane and 

 shrinks in size, it becomes possible to discriminate ripe 

 eggs from unripe ones. This is impossible in the, case 

 of the Oyster — the only available test is fertilization: 

 if the eggs do not develop they are unripe. After fer- 

 tilization, the eggs divides into a number of sequents 

 termed blasto:meres and out of these the future organs 

 of the animal are built up. 



It is characteristic of the eggs of all Mollusca, so far 

 examined, that a number of smaller blasto meres should 

 be budded off from one pole of the egg, out of which 

 are formed the skin and nervous system. In the Oyster 

 this is well seen; the peculiarity to notice is that the 

 rest of the egg remains undivided as one large blastomere, 

 whereas in oth2r Mollusca the whole egg first divides 

 into four equal parts when then bud off smaller blas- 

 tomeres. The larger blastomere however divides later 

 and forms a central mass of cells the rudiment of the 

 gut and internal organs, and this central mass covered 

 by the smaller cells. Soon the little larva rises to the 

 top and begins to swim, and it is then seen that there 

 is a hat-shaped anterior part surrounded by a thickened 

 belt of skin armed with powerful cilia. This organ is 

 termed the protoiroch, and is found in the young stages 

 of nearly all Mollusca and worms. About this time the 



