298 CRESS WELL SHEARER. 



impossible to distinguish the sex of the immature young 

 They develop at once on being laid, showing that they have 

 already been fertilised within the body. Even when the 

 female is isolated in pasteurised sea-water the eggs develop 

 immediately on being deposited ; no sperm can therefore 

 fertilise them in the sea-water. 



The egg-laying is done at night, as every morning fresh 

 capsules are to be seen adherent to the coatings of the lobster 

 " berr}'," The eggs within these are always in segmentation 

 or gastrulation stages. They are laid in great numbers, so 

 that it is easily possible to obtain all the stages of develop- 

 ment up to the time the young worm leaves the capsule. 

 Development is direct and would seem to be rapid, for by the 

 end of the fortieth hour the young are fully formed and 

 appear ready to quit the capsule. On leaving this they move 

 about the gill-chamber or pass immediately to the lobster ova, 

 where they soon attain maturity. They are readily distin- 

 guishable at this time by their small size and the undeveloped 

 condition of the generative segment. The young of both 

 sexes resemble the female in shape. Van Beneden (2) has 

 figured a number of the young stages, and Haswell (13) 

 mentions that he has obtained a number of the stages in the 

 development of Stratiodrilus. 



Eegarding the nephridia, Foettinger (8) stated that in the 

 male there were five pairs of these organs, while in the female 

 there were four. Each nephridium consisted of an intra- 

 cellular tube running backwards on the border of the longi- 

 tudinal muscle-strands. They turn in sharply towards the 

 median line, to terminate ventrally, on the surface of the 

 succeeding segment to that in which they arise, in a small 

 pore. He could observe no internal openings or funnels. 

 Their heads at their point of origin are on the dorsal surface; 

 since they terminate on the ventral surface they run back- 

 wards in an oblique plane between the dorsal and ventral 

 muscle-bands. The first pair arise in the neck segment close 

 to the head, and run backwards to terminate on the ventral 

 surface of the second segment. The second pair arise in the 



