47 



cumference. It is more common in the male gonad, but 



is present also in the female. 



The parenchymatous tissue between the tubules has 

 nmch the same characters as in Stage I., but it is now 

 arranged in a more even system of bars and is not so 

 massive. Certain appearances, such as the difficulty of 

 distinguishing the limits of the growing tubules in relation 

 to the surrounding reticulum, seem to indicate that the 

 gonads grow at the expense of this tissue, or at least 

 absorb it during the process of growth. It was, however, 

 impossible to demonstrate this with certainty in the pre- 

 parations studied. 



Eipening of the gonads proceeds slowly from now on to 

 the end of January, and consists of a gradual increase in 

 the width of tlie already-existing tubules and of the for- 

 mation of side twigs. The contents of the tubules slowly 

 increases, and it must be understood that from November 

 onwards theie is an increasing number of free and 

 apparently mature ova and spermatozoa in the gonads. 

 The fact that moving spermatozoa may be obtained from 

 the mantle at the end of the year has been already referred 

 to. Whether the genital products present in the gonads 

 at the end of the year are fully mature and are capable of 

 development is uncertain, but if so, the presence of free- 

 swimming larvae in the sea about this time juay be easily 

 explained, since ova and spermatozoa may be swept out of 

 the lower partially ciliated tubules, and fertilization may 

 result. But a certain time may also be required for the 

 complete maturation of the genital products after tlieir 

 proliferation from the germinal epithelium. 



Stage HI. (PI. II., figs. 1, 2).— About this time the 

 mantle lobes liave attained the maximum of thickness, and 

 the gonads have invaded every part of the body un- 

 occupied by the other organs, even the outer wall of the 



