SEA-FISHERIES LABORATORY. 277 



between May and August, so that from Milroy's results, the 

 percentage of glycogen rises from December to within a month 

 or two of spawning. Mitchell* obtained glycogen in American 

 oysters in quantities which he states to be similar to those of 

 Milroy, and he also gives the spawning time as July and 

 August. The rise in glycogen in late summer is similar in the 

 oyster and mussel, but from December the variations in the 

 two animals do not show agreement. For several months before 

 the oyster spawns, the glycogen content of the animal is steadily 

 rising and, although a decrease sets in before the spawning 

 takes place, the minimum is not reached until this season is over. 

 With Mytilus there is a rapid fall of glycogen from December 

 to March, and then a tendency on the whole to a rise until the 

 time of spawning in April. It is of the greatest interest to 

 examine the sections stained for glycogen during this period. 

 In September, although the mantle may be comparatively 

 thick (24 mm.), there is no sign of reproductive products in 

 the connective tissue ; mantle thickness is not necessarily an 

 index of increasing sexual maturity. The glycogen is seen as 

 solid lumps lying in the connective tissue cells. From October 

 onwards, the egg and sperm sacs ramify through the tissue, 

 increasing apparently at its expense, and grow until they almost 

 impinge one upon the other. The glycogen, along with fat 

 globules, is seen to be wedged into the surrounding tissue. 

 Apparently one reason why there is less glycogen now is because 

 the sperms and eggs take up the space occupied by the former. 

 It is to be expected that such rapidly-growing tissue requires 

 nutriment, and there is little doubt that they obtain the latter 

 at the expense of the fat and glycogen ; but whereas the 

 former becomes incorporated into the reproductive products, 

 so far as micro-chemical methods are to be relied upon, there is 

 no conclusive evidence that this is the case with the glycogen, 

 as such ; it is apparently converted into some other substance. 



* Mitchell, loc. cit, p. 481. 



