Development 93 



paraffin. Sections of the body and of the limbs showed the 

 cercarisB at all stages of entry. They were found in the act of 

 passing through the unbroken skin, and not through the pores or 

 hair-follicles {vide figs 48 to 54). 



The cercarise seemed to be attracted by the warmth of the 

 body, as similar evidence was rare in a recently dead mouse similarly 

 immersed and the degree of penetration slight. 



Development in the Definitive Host. 



Once the cercaria has entered the definitive host it undergoes 

 no further metamorphosis. There is gradual growth with differen- 

 tiation of organs, and in Bilharzia with differentiation also of male 

 and female individuals. The males are early recognizable from 

 the females by their greater breadth and the stouter formation of 

 the ventral sucker. In the accompanying plates is figured, under 

 the same magnification, at the various stages, the gradual develop- 

 ment of the adult body in all its phases from the cercaria before 

 it enters to the paired egg-producing adults some months later. 

 The route taken by the cercarial body in its transit from the skin 

 to the portal system is still under investigation. It is noteworthy 

 here, however, that the cercariae do not all appear to arrive in the 

 liver at the same time. Some of the smallest forms were obtained 

 by teasing liver which contained also forms almost fully grown. 

 This accords with Professor Looss's experience in ankylostome 

 infection. A number of larvas probably become " lost " in the 

 tissues. It may be, however, that a certain number enter the blood- 

 stream direct, while others pass first through the lymphatic system. 



