PHYSIOLOGY OF REPRODUCTION AND 

 DEVELOPMENT. 



VARIETIES OF GENERATION. 



Abiogenesis (Spontaneous or Equivocal Generation). Even until modern 

 times it was believed that inanimate substances, derived from the decomposition 

 of organized matter, could under certain conditions again be transformed spon- 

 taneously into living matter. While Aristotle believed that spontaneous genera- 

 tion could be extended to include the insects (vermin) , the few modern adherents of 

 this theory applied it only to the lowest forms of life. As a result of much research 

 along this line it has been demonstrated conclusively that when organized matter 

 is subjected to a high temperature (200 C.) within hermetically sealed tubes and 

 all bacteria therein are actually destroyed, spontaneous generation cannot take 



,( 



FIG. 345. Ovum from the 

 Uterus of a Sexually Ma- 

 ture Proglottis of the 

 Taenia solium: a, albu- 

 minous envelop; b, remains 

 of the accessory yolk; c, 

 embryonal shell; d, embryo 

 provided with embryonal 

 hooklets. 



FIG. 346. Encapsulated Cysticerci (from 

 Taenia solium) in the Flesh of the Sartorius 

 Muscle in Man. Natural size. 



a 



FIG. 347. Cysticerci from 

 Taenia solium, with their Con- 

 nective-tissue Capsule Re- 

 moved: i, natural size; 2, 

 enlarged with a magnifying 

 glass; a, embryonal vesicle; 

 b, the hollow bud produced 

 by sprouting from the em- 

 bryonal vesicle; c, suckers 

 and crown of hooklets of 

 the head of the tapeworm. 



place. This fact sustains the doctrine that all life is derived from previous life 

 ( pmne vivum ex ovo " or " ex vivo ") ; or as Harvey says: ut omnibus viventibus 

 pnmordium insit, ex quo et a quo proveniant. 



It is a noteworthy fact that even some of the higher invertebrates (gordius, 



anguilula tardigrada, rotatoria) may, when kept dry for some time, apparently 



e and lie dormant for a considerable time, but when supplied with moisture 



lay be resuscitated anabiosis. Rotatoria (wheel-animalcules) recovered after 



oeen kept in a dry vacuum for eighty-two days, and immediately after 



exposure for thirty minutes to dry heat at a temperature of 100 C. Rotatoria 



sd gradually in their natural habitation proliferated when again moistened after 



938 



