88 OF THE ANATOMY AND DEVELOPEMENT 



a surface, or from other causes, as during its increase in size to 

 rupture, then the young escape, and so form new and altogether 

 independent animals. As the hydatid is by no means of unfre- 

 quent occurrence in the liver and other internal organs, this limi- 

 tation of the increase appears to be a beneficent law of nature, 

 for the purpose of preventing the fatal termination which the 

 rapid increase of these animals would infallibly produce. In Dis- 

 kostoma we have an instance of this rapidity of reproduction, 

 which happily appears to be of rare occurrence. 



It may be well to state here also the opinions to be deduced 

 from the changes which take place in the germinal membrane of 

 Acephalocystis, and the other acephalic entozoa. It has been 

 already fully described in what manner the function of reproduc- 

 tion in these animals is stopped, namely, in consequence of the 

 thickening of the germinal membrane. After having made out 

 this fact, I was led to infer that many instances of the stoppage 

 of cellular formations at certain periods of life might be traced to 

 similar changes taking place in the germinal membrane of the 

 formative organ, and, with the view of determining this point, 

 examined the testes of several old men, after the fecundating 

 power had in all probability passed away, when the germinal 

 membrane in almost all cases had become thicker and quite dif- 

 ferent from what is generally seen in young males, a change 

 which (as we have attempted to describe) had taken place in the 

 germinal membrane of hydatids.* 



IV. OF SPHAIKIDION.f 



Sphairidion aceplialocystis is an animal allied to Acephalocystis, 

 chiefly from its acephalic character, but also from its reproduc- 

 tive organ being enclosed within the centre of its sac. This re- 

 productive body or membrane is exactly similar to the pedicle of the 



* The stoppage here alluded to, in the function of reproduction of these animals, may 

 be also greatly assisted, and the degenerating process made more active, in consequence of 

 the thickening of the external membrane preventing the absorbing cells extracting from it a 

 sufficient supply of nourishment. 



f 2<p#/(/^OJ/, a globule. 



