of the Fishery Board for Scotland. 225 



June 3, 1987. — Some pond mussels had been kept in aquaria in order 

 that the spawn might be observed. Up till this date none had been 

 noticed. The mussels were examined and found to have red ovaries. 

 The yolk granules poured out of the egg. The zona appeared to 

 be two-layered. The nucleus seemed to be simply a naked sphere of 

 clear protoplasm. Sperms were obtained from a dirty-yellow or amber- 

 coloured mautle. 



June 25, 1907. — Some mussels were obtained through the kindness 

 of Professor M'Intosh, from St. Andrews. 



The mantle of the mussel had its central part tilled with reproductive 

 elements, but showed surrounding that portion a more or less broad clear 

 margin. In the female the sexual part was orange-coloured, and in the 

 male whitish. A larger proportion of the mantle was, in most of the 

 cases examined, filled in the female than in the male. The thin 

 dark-orange mantle (female) showed little white bodies all over the 

 orange groundwork. In the male the white bodies were not so distinct, 

 but larger, measuring about ^L-inch. The eggs were of the usual 

 type of the unripe egg, having a big pore from which the yolk granules 

 pour, and having a nucleus with a sharp outline. The zona was all 

 crumpled, and evidently consisted of two layers. 



In the spermaries there were bodies similar to the heads of sperms 

 consisting of a circular head with a tapering manubrium- like prolongation. 

 Several groups of these were seen united by the ends of their 

 manubria. 



June 28, 1907, — Some of the St. Andrews mussels were examined 

 on this date. Several males measured from 2 ins. to 2| ins. in length. 

 The mantle was about ^^^-inch in thickness, and was only partly 

 occupied with reproductive organs. The females, measuring 31 ins. to 

 3| ins., showed thin mantles, which, as in the males, were not fully occu- 

 pied by the ovaries. 



July 16, 1907. — A mussel which was examined on this date had red 

 ovaries approaching ripeness. The reproductive organs were restricted 

 to part of the mantle. 



July 19, 1907. — Six mussels from the pond were examined on this 

 date. They belong to the lot which was sampled in April. They 

 measured from 2-2| inches. One of them is shown in figs. 103 and 104. 

 Five were males, the sixth was a female. 



The mantle of the male mussels was in some cases of a light cream 

 colour, in others of a dark cream colour. I'ractically the 

 whole of the mantle, with the exception of a small portion at 

 the anterior lower side, was occupied with the cream-coioured 

 organs. The mantle was about gth inch in thickness. The organ is 

 thinner towards the margin. The spermaries were not so prominent. 

 The mantle shows an uniform cream-coloured surface, which under a lens 

 is seen to be broken up into little roundish bodies. It differs from the 

 condition seen earlier in the year. On cutting into the mantle a whiteish 

 fluid issued ; it consisted wholly of ripe sperms. Where a portion of the 

 tissue was teazed and pressed out under a cover-glass a delicate network 

 tissue which resembles vessels, and having associated with it groups of the 

 heads of sperms stuck together, was made out. The sperm heads had the 

 manubrium-like process but no tails. The tissue consists of vessels, 

 stringy fibres, and fairly large pouches crowded with heads of sperms 

 Ihere are also some round cells in the pouch ; they are larger than the 

 heads of the sperms : they may be gland cells on the wall of the pouch. 

 On dissecting the abdominal process ripe sperms, with tails, clear 

 corpucles (fat), and groups of cells showing ranular contents were found ; 



