of the Fishery Board for Scotland. 



223 



second mussel had a cream-coloured mantle. It had brown veins, and was 

 crowded with minute corpuscles which looked like the heads of sperms. 



December 15, 1906. — The mussels supplied by the merchant were of 

 two distinct colours, viz., (1) light cream mantle, and (2) dark cream, 

 inclining to orange. In the first class, on teazing a portion a white fluid 

 is obtained that coagulates on the add ir ion of fresh-water. The mantle 

 consists of a very slight stringy tissue ; hardly any basement or ground- 

 work tissue is made out. The principal constituent is very minute 

 oscillating corpuscles (fat) and pitcher-shaped cells full of larger 

 corpuscles. Some round cells with large nucleus and nucleolus were also 

 noticed. In one or two of the main vessels little brown patches were 

 seen. 



In the second lot a slight milkiness, due to fatty corpuscles, was 

 obtained on teazing a portion of the mantle. Pouches were made out, 

 with large dividing cells, and also some bodies apparently glandular, 

 showing a central cavity and a great number of minute cells. 



January 21, 1907. — On this date the mussels supplied to the Labora- 

 tory were separated into two classes by the colour of the mantles — (1) a 

 cream-coloured mantle, and (2), an orange-coloured mantle. There are 

 others which have a pink-cream hue. Some have thin orange-coloured 

 mantles. In large specimens the orange-coloured mantles are thick, and 

 show traces of a creamy-coloured base. 



On cutting into the creamy-white mantle a pale white fluid issues 

 Under the microscope it is seen to consist of ruptured thin-walled 

 capsules, and there are also minute bead-like corpuscles and oil 

 corpuscles. 



In the orange mantle there are little brown cells of various sizes 

 mostly minute. They show a nucleus. 



The mantle of a small mussel was full of brown capsules filled with 

 brown corpuscles of various sizes, and also of colourless corpuscles. The 

 brown corpuscles are in most cases very small ; some larger were seen to 

 be dividing. The brown corpuscles are attached in little groups. There 

 is a colourless connective tissue with long cells and an apparently 

 albuminous blood fluid. The capsules appear to be full of an albuminous 

 corpusculated fluid, in which the brown corpuscles are growing. 



In the large mussels the capsules are not so brown, but the brown 

 corpuscles are dividing. There are also present colourless cells with 

 nuclei. 



February 27, 1907. — The mussels were now distinctly yellow (male) 

 and red-coloured (female). The red colour was in various stages. 



The male mussel was not very far advanced ; the spermatophores con- 

 tain round corpuscles, which oscillated very vigorously ; they were of 

 all sizes. 



April 11, 1907. — Some mussels that were shelled on the previous day 

 were examined on this date. The cilia in some were still working. 



The male had a pale mantle with the spBrmaries forming a prominent 

 white granular layer on it. The paler part is seen to be divided up with 

 pale-coloured spermaries, and the^e are sacs full of sperms, not quite so 

 large as the white sacs. The white sacs are large and more widely 

 separated from one another than ate the egg-sacs in the female. 



In some females the ground-work of the mantle is orange-coloured; the 

 ovaries are white. The fringe of the mantle is distinctly orange-coloured, 

 and shows brown bodies in vessels. In another female the mantle was 

 not orange-coloured, but it had small closely-packed egg-cases and similar 

 brown bodies. The eggs are quite white, pitcher-shaped, with a well- 

 marked nucleus, possessing a nucleolus. The nucleus, as Wilson pointed 



