226 BULLETIN OF THE BUREAU OF FISHERIES. 



In Narragansett Bay and Long Island Sound mussels usually reach this condition in the 

 late winter or early spring, while in the more open waters of the ocean, such as along the 

 south shore of Long Island, they do not attain it until June or July. 



Following the maximum development of genital tissue there is a shedding of the 

 reproductive elements that leaves the bod} 7 in a shrunken condition and with a compara- 

 tively large and conspicuous dark-green liver. Such shellfish are unattractive in appear- 

 ance and undesirable for use as food. This change takes place in the mussels of Narra- 

 gansett Bay and Long Island Sound during the months of June and July, or sometimes 

 as late as August, according to the depth of the water in which the beds lie. Those in 

 shallow water subject to the higher temperatures, direct rays of the sunlight, and wave 

 action are the first to spawn, while those in very deep water are the last to begin the 

 process, or they may even retain the genital products throughout the season and absorb 

 them as reserve food. Such mussels are nearly always in good condition. 



Mussels on the south shore of Long Island put on flesh and mature their reproductive 

 elements in the late spring and early summer, coming into prime just as the Narragansett 

 Bay and Long Island Sound mussels go out of season. They continue in marketable 

 condition until the latter part of September. 



From Narragansett Bay and Long Island Sound, on one hand, and the south shore 

 of Long Island, on the other, there may be obtained a continuous supply of marketable 

 mussels from March to October. This fact is of much significance, for since the mussel 

 season supplements that of the oyster it offers an opportunity to oystermen to keep 

 their expensive equipment busy the year round in case a mussel industry is established. 



The series of structural changes which occur during the year are illustrated in the 

 photomicrographs of cross sections taken through the mantles of mussels from Woods 

 Hole, Mass., during the months of December, January, April, June, and August (figs. 212 

 to 220). The figures are all represented on a uniform scale of 30 diameters magnifica- 

 tion, so that the relative thickness and condition of the mantle at the different seasons 

 may be compared at a glance. 



On December 1 the mantle of a female mussel was found to be composed of a rather 

 uniform reticular tissue, with blood vessels running just below the outer surface and 

 small genital canals and follicles extending to a slight extent throughout the middle and 

 inner side (fig. 212). On the same date the mantle of a male mussel was found to be 

 thinner, but the follicles were much more completely formed and were filled with devel- 

 oping spermatozoa (fig. 213). 



Six weeks later the mantle of a female mussel was found to be thinner than that 

 of the specimen examined December 1, but the genital canals and follicles were more 

 numerous and better developed (fig. 216). On the other hand, the mantle of a male 

 mussel taken on the same date was thicker than that of the male specimen examined 

 on December 1, and the tissue was firmer and less vacuolated (fig. 217). 



During the next three months considerable increase in growth was found to have 

 taken place in the tissue as well as the formation of large numbers of genital cells in 

 both the female (fig. 219) and the male (fig. 220). 



The maximum development was found in the middle of June when the female 

 mantle in particular was distended with the reproductive products (fig. 214). 



Shortly following this condition, spawning takes place and practically all of the 

 genital elements are shed, which results in a decided shrinkage of the mantle and other 



