190 



ENTOZOA. 



larva (Nurse, Sporocyst, or Redia, as the case may be). What- 

 ever be tlie full significance of these internal developments, we have 

 at least satisfactory evidence that the complete and fi-ee embryo is 

 a globe-shaped animalcule, having the anterior third or cephalic end 



Fig. 40. — Free embryo of Distoma lanceolaticm j highly magnified. — Leuekart. 



of the body covered with cilia, and armed with a central boring spine. 

 In consequence of this limitation of the ciliated covering, its swimming 

 movements are less vivacious than those of the embryo of Faseiola 

 hepatica ; it will, therefore, probably take up its residence in a less 

 active host than that chosen by the embryo of Faseiola, selecting one 

 of those molluscs which either move slowly or are prone to keep at 

 the bottom of the water. The mature eggs have a length of els to 

 6^5 of an inch, and a breadth of ^'. The long diameter of the free 

 embryo varies from ^ ' to ^ , the transverse diameter being j^". 

 Whilst the embryos were still in the Qgg Leuekart could see no 

 ciliary motion ; with most observers, both the ciliary apparatus and 

 the boring spine appear at this stage to have altogether escaped 

 observation. 



The further transformations of the embryo and larvse of 

 Distoma lanceolakom are not known with certainty, but our conjec- 

 tures on tliis score cannot be far removed from the actual truth. 

 We shall probably find that the embryo changes into a Sporocyst, 

 the latter producing, directly or indirectly, a colony of armed cer- 

 carian larvge provided with tails. These higher larval forms may 

 again inhabit moUuscs, after a longer or shorter period of active 

 wandering, being subsequently transferred along with their hosts 

 into the intestinal canal of herbivora, and, in a few cases (probably 

 along with watercresses) into the human stomach. Leuekart 



