LINEUS. 263 



membrane. It is possible, however, that they may be due 

 to shrinkage in the process of preservation. As has 

 already been seen, the only space of this kind which occurs 

 in Lineus gesserensis is a small one between the proboscis 

 sheath and the oesophagus. The space between the intes- 

 tine and the inner longitudinal muscle layer is small, and 

 is occupied by connective tissue cells and their inter- 

 cellular substance. 



In this space occur sacs alternating with the 

 intestinal diverticula (PI. III., figs. (J and 8), and 

 with the intestinal diverticula (PI. III., figs. 6 and 8), and 

 lined by connective tissue cells. These are the gonads 

 whose cavity, apparent in the young animal, becomes 

 obliterated in the mature worm by the sexual cells which 

 fill it, and which are probably derived from the connective 

 tissue cells which form its lining. Each gonad possesses 

 a duct which opens dorso-laterally (PL III., fig. 8, gd.), 

 and which is formed partly by a prolongation of the con- 

 nective tissue lining of the gonad, and partly from an 

 ectodermal depression. 



The sexes are separate, and in the breeding season, 

 which lasts from about February till June, the 

 female deposits her ova under stones in a long 

 tubular gelatinous cord. In the walls of this cord are the 

 ova contained in small flask-shaped transparent capsules 

 (PI. III., fig. 7). One of the gelatinous cords produced 

 by a single female usually contains a hundred or more of 

 these little capsules, and each capsule contains the con- 

 tents of a gonad, i.e., from one to seven ova, according to 

 the size of the female. The spermatozoa of Lineus 

 gesserensis possess a long pointed head (PI. IV., fig. 4). 

 The gelatinous cord containing the ova is said to be the 

 joint production of the male and the female. Into it the 

 male then proceeds to discharge spermatozoa. Soon 



