168 



ENTOZOA. 



measuring individually 2^0". The epidermis has a thickness of g^". 

 In the central parenchymatous mass no internal organs are distin- 

 guishable, but Leuckart observed faint indications of a canal 

 toward the hinder part, the caudal extremity sometimes displaying, 

 he thought, evidences of a cleft, as if there were an opening. 



Fig. 38. — Ciliated free swimming embryo of Fasciola hepatica. — Leuckart. 



As long as the ciliated covering remains intact, the embryo, 

 like other animalcules, displays great activity, whirling round and 

 round on its own axis, and also describing gyrations and circles in 

 the water of different degrees of range, the latter movements being 

 accomplished by bending the body upon itself to a greater or lesser 

 curvature. We have seen Stentor and other infusoria exhibiting 

 the same behaviour, and, as Leuckart observes, with his newly- 

 discovered embryo, when these creatures knock against any obstruc- 

 tion, they pause after the blow, as if to consider the nature of the 

 substance they have touched. In the case of the fluke embryo the 

 ciliated covering eventually falls off, when the embryo re-assumes a 

 more or less oval figure, at the same time changing its swimming 

 mode of progression for the less dignified method of creeping. In 

 the free ciliated condition the embryo of the common liver-fluke 

 measures, according to Leuckart, i^" in length, the anterior broad 

 end being m"- The ciha have a longitudinal measurement of iw"' 



Up to the time at which I write, the subsequent changes which 



