DEVELOPMENTAL STIMULI IN THE CESTODA. 135 



scattered. The short period between the first contact with the 

 outer water and the egg-laying indicates that the infection of the 

 intermediate host is, by means of countless embryos, developed 

 in the open ocean and not by the eating of the intact proglottids 

 with their contained eggs. 



EGG DEVELOPMENT. 



On collecting the eggs laid by proglottids in the laboratory 

 and placing them in dishes in which the sea-water can be kept 

 reasonably pure, development ensues as far as the six-hooked em- 

 bryo stage which I have represented in Fig. 8, drawn from the 

 living specimen. I did not succeed in obtaining embryos be- 

 yond this stage, and therefore cannot say whether the embryo 



B 



FlG. 8. Six-hooked embryo of Crossobothriuni laciniatuw. m, egg membrane ; 

 r, remains of outer envelop ; e, ectoderm of Schaunisland ; />, six-hooked embryo. 



enters the next host in this condition or as a ciliated larva (Schau- 

 insland, " Bothriocephalidae,'' '86) which subsequently hatches 

 from the embryo figured. 



In the common Tsenias and those Cestodes which have simi- 

 lar hosts and conditions of life-history, the fertilized eggs on 

 passing into the uterus develop there into six-hooked embryos 

 and remain in that stage until they reach the tissues of the in- 

 termediate host. In the Bothriocephalidae, Schauinsland de- 

 scribes B. rugosits 'as having such an intra-uterine development 

 as far as the six-hooked embryo, and B. latus, Trianophorns 

 nodnlosus and Ligula siniplissiuia as producing eggs which de- 

 velop only when they reach the water. In the last three species 

 the eggs accumulate in the uterus in the condition of resting 

 oosperms surrounded by their yolk and the egg-shell, but do 

 not develop until they are laid in the water by the parent pro- 

 glottid after this has left the host's intestines. 



