44 



PARASITES OF MAN 



connection just referred to; and when, at length, the ciliated 

 animalcule has succeeded in overcoming this first difficulty, it is 

 ludicrous to witness its frantic efforts to find 

 an opening in the shell. While thus par- 

 tially liberated, it will rush to and fro from 

 one pole of the egg to the other, performing 

 a series of summersaults, and at the same 

 time occasionally rolling itself over laterally. 

 This activity becomes gradually more and 

 more violent, until at length its excitement is 

 worked up into a sort of frenzy. I have many 

 times watched these performances, which, 

 however, are only to be seen within those ova 

 whose shells, for some reason or other, refuse 

 to yield to the earlier aud ordinary efforts of 

 the prisoner. In all cases where these phe- 

 nomena are witnessed the eye readily detects 

 a number of small free globules between the 

 embryo and the inner wall of the shell (fig. 

 13). These minute particles are likewise 

 tossed about tumultuously during the rapid 

 rotatory movements of the imprisoned larva. 

 Except as regards their size, these globules 

 do not differ in character from the sarcodic 

 contents of the animalcule. They are pro- 

 bablv superfluous detachments from the pri- 

 mitive yolk-mass, but it is just possible that 



fa^ may a ff or( J gome a j^ { n ^ Q fi na l break- 



ing up of the shell. Whilst the embryo remains fixed its 

 tail is usually directed towards the narrower or spine-bearing 

 pole of the egg, but in a few instances I have seen this position 

 reversed. As regards the precise mode of emerging from the 

 shell, and the time occupied by the larva in freeing itself, there 

 are several points of interest. Speaking generally, the purer 

 the medium into which the ova are transferred, the more rapid 

 will be the movements of the larvae. To give an example of 

 observed facts in relation to the rapidity of development, I cite 

 the following : " On the 20th of August, 1870, I placed twelve 

 eggs of Bilharzia under the microscope. The medium in which 

 they were immersed consisted of eight parts of ordinary 

 drinking water to one of urine. At the expiration of seventeen 

 minutes the first-born made its escape. In the course of 



developed. Original. 



