12 ANIMAL PARASITES. 



The thinner the shells are the more readily do the eggs alter 

 their form. Thus the eggs of T. solium acquire a funnel-shaped 

 or cup-like hollow when placed in strong spirits (by extraction of 

 water) ; this I had overlooked in previous investigations, as 

 Lcuckart has pointed out. The mode of formation of these shells 

 will be subsequently described. 



We have now, in the first place, to speak of the subsequent fate of 

 the egg-envelopes or shells and the embryos enclosed in them, and for 

 this reason refer to what has been said (Section I) with regard to 

 the migration of the proglottides and their subsequent fate in the 

 outer world, and respecting the exclusion of the eggs from the 

 intestine and the eggs which occur isolated in nature. The next 

 thing that happens to the eggs, whether enclosed in the proglot- 

 tides or freely disseminated, is that they are swallowed with the 

 above-mentioned grasses, with roots and fruits which are eaten 

 without peeling, or lastly with drink, by different herbivorous 

 or omnivorous animals (including man). Tliey thus pass the 

 mouth and oesophagus, and then reach the stomach, in most cases 

 certainly uninjured ; here the egg-shells, which have become 

 softened in the digestive fluid, partly in consequence of the 

 digestive process, which acts first of all and principally upon the 

 inner stratum of the egg-shell, and partly in consequence of 

 friction, burst against other solid alimentary substances, by which 

 means, of course, the embryo is set free. Artificial experiments 

 made by Leuckart on the digestion of proglottides and eggs, by 

 introducing them into the stomachs of animals kept at a hatching 

 heat, gave, as their ordinary result, after the digestion of the 

 proglottis itself, only a greater brittleness of the eggs ; it was 

 very rarely, and only in a few eggs, that Leuckart saw a breaking 

 up of the egg-shell ; but he only observed this once in greater 

 abundance in eggs of the Tcenia crassicollis, which he had exposed 

 to a hatching heat in an emulsion of the mucous membrane of 

 the stomach. But, on the contrary, if we examine the contents 

 of the stomach of a rabbit four or five hours after the adminis- 

 tration of proglottides or eggs (the animal should have fasted 

 previously for more than twenty-four hours), we find amongst the 

 contents of the stomach, uninjured, but extremely brittle eggs, 

 together with various remains of broken egg-shells, and, under 

 favorable circumstances, perhaps a free embryo here and there. 

 The rupture of the egg-shells, therefore, appears to be, as already 

 remarked, a consequence of the chemical action of the fluids of 



