350 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



shape of the mature gonad is indicated. They are both 

 somewhat pear-shaped, the broader end being attached to 

 the septum (PL I, fig. 2, ov.). In a mature worm, 

 however, the ovaries often attain so great a size that they 

 are somewhat bent round in the segment and the original 

 shape is lost : this is also partly due to the presence of 

 the oldest ova at one side of the ovary. The ovaries 

 persist throughout the reproductive season, and only 

 attain their full size when the rest of the reproductive 

 organs are developed. 



If, however, in a mature worm one seeks for the 

 testes, one will not be able to find them. This is due to 

 the fact that they have been completely enclosed in the 

 sperm sac, which is of large size and in which the 

 spermatozoa complete their development. It is necessary, 

 therefore, to examine much younger worms in order to 

 find the testes. In fact, they are quite well developed in 

 those individuals in which there is no trace of any other 

 part of the reproductive system except the ovaries. The 

 testes develop somewhat earlier than the ovaries, and, 

 therefore, in a young worm it will be easy to identify them 

 without verifying their position, as they will be larger 

 than the ovaries. When the testis has attained its full 

 size it consists of a mass of rounded cells with clearly 

 marked nuclei, but without any specially characteristic 

 features. These may be called the spermatogonia, or 

 sperm mother cells, and here the development of the 

 spermatozoa in the testis ceases. The spermatogonia must 

 be transferred to the sperm sac before further develop- 

 ment can take place. 



Many of the earlier writers confused the testis with 

 the sperm sac or with part of it. D'Udekem (1855), for 

 example, speaks of the testis as occupying segment 8 

 where it appears as an unpaired organ below the intestine 



