486 ANATOMICAL .SJN'D rATIIOLOGICAL OBSEKVATIONS. 



terminated ; — if, on the contrary, the parent hydatid be so 

 near 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 hy no 

 means of unfrequent occurrence in the liver and other internal 

 organs, this limitation of the increase appears to be a benefi- 

 cent law of nature, for the purpose of preventing the fatal 

 termination which the rapid increase of these animals would 

 infallibly produce. In Diskostoma 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 wliat manner the function of 

 reproduction in these animals is stopped, namely, in con- 

 sequence of the thickening of the germinal membrane. After 

 ha\T.ng 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 different 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.* 



* The stoppage here alliided 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. 



