DEVELOPMENTAL STIMULI IN THE CESTODA. 



133 



and then to pass out with the faeces, even though their early de- 

 tachment from its strobila may have been premature and caused 

 by the outward passage of the excreta or the contraction of the 

 intestine. 



The manner in which the egg-laying proceeds in any single 

 proglottid thus placed in sea-water is a very interesting thing to 

 watch. Extreme writhing movements of a quite definite sort 

 begin at once. The proglottid bends along its axis of breadth 

 until it is almost a closed ring, the pointed anterior end some- 

 times passing into the angle made by the posterior flaps (Fig. 2) 

 and thus reminding one of an acrobat who could bend backward 

 until his head should be thrust between his legs from behind, 

 then the proglottid straightens and the bend is reversed, it 



uo 



uo 



FIG. 6. Proglottid in the act of egg- 

 laying seen from the side. Lettering same 

 as for Fig. 7. 



FIG. 7. Proglottid at close ot egg- 

 laying seen from anterior end. a, an- 

 terior end ; /, penis ; g, groove marking 

 outline of uterus ; uo, ruptured area 

 through which the eggs escape. 



straightens again and bends into the first position and so on ; 

 these motions continue until the nipple-like prominence of the 

 protruding body bursts and the liberated eggs gush forth. When 

 the break occurs the extreme violence of the writhing ceases and 

 the proglottid bends backward rather more than forward (Figs. 6 

 and 7) until all the eggs have been expelled, when a gaping 

 hole is presented (Figs. 6 and 7) where once was the distended 

 uterus. Even when there is hardly an egg left within it, the 

 straining movements of the proglottid continue as though it were 

 making sure that not a single egg remained. Figs. 6 and 7 

 represent proglottids in which the egg-laying had been almost 



