of the Fishery Board for Scotland. 227 



surface of the mantle in one specimen. The reproductive elements 

 were, however, usually hid by the fat condition of the mantle. The 

 mussels which contained ripe sperms had mantles of the following 

 colours : — wdiite, light cream, and deep cream. In the females con- 

 taining full-sized eggs the mantles were coloured while, cream, and 

 yellow, with, in each case, a pinkish tinge, and dark-red. When the 

 mantle of the male mussel is cut across the section is yellow, and from 

 it a white fluid oozes. In the female the section is brown-mottled. 



On November 2, two females were examined in which tlie reproductive 

 organs were quiescent. In the first case the mantle was of a deep 

 orange-red or chocolate, a colour nearly resembling that of a ripe mussel. 

 The tissue was mottled with brown corpuscles. The body fluid that 

 issued on teazing a portion of the mantle consisted of minute clear drops. 

 In the second case the mantle was of a light yellow colour, 



M'Intosh examined mussels from January to July. In January 

 " the mantle was, when compared with an undeveloped specimen, 

 considerably thicker. A male measuring 3^ irohes in length presented 

 in the thickened generative region large, pale, round sperm-sacs filled with 

 minute spermatozoa, which have minute ovoid bodies with finely filamen- 

 tous tails. They are lively and tenacious of life, . . . The female 

 had the same region of the mantle crowded with a prodigious number of 

 minute ova. In shape they are ovoid, with a transparent investment and 

 an inner granular yolk with a pale circular area. In February the 

 mantle . . . increased considerably in thickness. The whole surface 

 of the mantle became speckled in both sexes with the reproductive 

 elements. . . . The mantle in one case had increased in thickness 

 to about |-inch, and the development of the sperm-sacs seemed to proceed 

 from the dorsal to the ventral edge of the mantle. Even in specimens 

 in which the shell has been injured and the mantle remains thin at 

 certain places, an immense number of ova are developed. After full 

 maturity is obtained, as in April, the orange mantle is richly marked in 

 an aborescent manner by racemose sperm-sacs and ducts, especially 

 towards the margin, and when the mantle is swollen out with water the 

 sperm-sacs project like bunches of grapes. In the female this appearance 

 is not so evident, for the ova are grouped in masses of a circular or 

 ovoid form and densely packed. The females at the end of May now 

 contained comparatively few ova, and the mantle had diminished consider- 

 ably in thickness. Much granular brownish pigment was present in the 

 latter. On the 9th June the female mussels still showed some ova in 

 the thickened dorsal region of the mantle, but the margins were pale and 

 thin. As before, much brownish pigment was present. In July the 

 dendritic appearance of the salmon-coloured mantle was less marked, and 

 neither ova nor spermatozoa could be distinguished microscopically. 

 The general stroma was granular and minutely cellular, as if a general 

 resolution of the tissue were taking place, and the characteristics of the 

 sexes were absent." 



The eggs would, then, appear to be derived from the minute brown- 

 coloured cells seen in the mantle of the unripe mussel. The thick fat 

 mantle is not a necessary precursor to reproductive activity. The little 

 brown cells seem to be supplied with chlorophyll, and are found at the 

 end of the year in thin mantles as well as in fat mantles. Any one 

 lot of mussels consists usually of a mixture of fat and thin mantles, 

 showing that even where the water may be abundantly supplied with 

 food some mussels may still, from the accident of their situation, be 

 starved. In one case the sample may show a majority of fat, in another 

 a majority of thin mantles. 



