i] PERIODICITY IN CONVOLUTA 27 



large glass vessel, hundreds of egg-capsules may be 

 obtained within a few days. The laying continues 

 for a week or more and then, when the time of the 

 slack tides arrives, it ceases, even though some of 

 the animals are yet carrying mature eggs. After a 

 barren fortnight, egg-laying begins again. Both the 

 animals which failed to bear and those which pro- 

 duced eggs contribute to the fortnightly crop. The 

 mode of egg-laying of C. roscoffensis is in some 

 respects peculiar. Occasionally, the eggs are dis- 

 charged separately one or two at a time ; but more 

 often they are contained, as has been stated, in a 

 common, gelatinous capsule. It happens frequently 

 that oviposition results in a rupture of the tissues 

 of the parent. The body becomes torn and may even 

 break across the middle. The anterior end crawls 

 away and, behaving like an intact animal, heals its 

 wounds, regenerates its lost parts and recovers 

 completely. The tail end remains near the egg- 

 capsule, and exhibits ceaseless, revolving, "circus' 

 movements, swimming in devious spirals ; then it 

 comes to rest and finally disintegrates. Unlike 

 C. paradoxa, C. roscoffensis is slow in hatching. 

 After about four days, the larvae begin to revolve 

 actively within the capsule-membrane, then at the 

 fifth to the seventh day after the eggs were laid, the 

 egg-membranes split equatorially and the society of 

 larvse is set free to creep and swim within the common 



