Hoivard. — A Second Generation of Mussels 91 



byssus-gland located on the ventral and posterior median 

 edge of the foot. I have observed this thread in mussels 

 under 3 mm. and it was found as late as the end of the 

 first year in this culture. A month later no further trace 

 of it could be found. 



During the second year, noticeable features were the 

 rapid growth and the appearance of sexual differentia- 

 tion in secondary sexual characters. Modifications of the 

 gills to form the marsupium appeared in the female to- 

 gether with the corresponding fullness of the shell over 

 that organ. For growth the maximum length of shell 

 observed was 62.8 mm. (about 2y 2 inches) nearly double 

 that of the first season (32 mm.) measured in November. 

 To test the commercial value of shells at this age buttons 

 were cut from a few. A 16 line button, 2 lines thick, was 

 produced. This is rather too thin for commercial pur- 

 poses but it shows that a growth of two years is quite 

 appreciable. 



The middle of August of this year, the third summer, 

 the first gravid mussels were found. This, the first ob- 

 served breeding date, was two years, two months, and 24 

 days from the date of implantation of the larval mussel 

 upon the fish. All females, as far as examined, were 

 found to be gravid ; these were picked up at random from 

 the crate so the indications are that breeding is general 

 at this age. The glochidia were mature in some individu- 

 als on August 14th and near maturity in others, which 

 from the date of the last observation would fix the time 

 of ovulation as July. Mature glochidia from these mus- 

 sels were taken and an implantation obtained on a 

 number of fish. The first free juveniles after metamor- 

 phosis were obtained in ten days, others remained as late 

 as the 18th day, a rather long period of shedding. The 

 juveniles secured represent the second generation of 

 mussels, but the life cycle was completed when glochidia 

 were mature, as that was the stage with which the ex- 

 periment began. 



A comparison was made of a crate-grown shell with 

 one grown in nature. In these two mussels of the same 



