THE DOCTRINE OF IMMORTALITY 55 



ovum. Hertwig investigated various species of eggs and 

 observed the same fundamental phenomena in them all. 

 Out of the head of the entering spermatozoon there arises a 

 nucleus-like structure or pronucleus. Before or during 

 impregnation the nucleus of the ovum loses a portion of its 

 contents by a process which we call the phenomenon of 

 maturation. The part of the nucleus of the ovum which 

 remains forms the female pronucleus. The two pronuclei 

 unite and form a new complete nucleus. The fertilization 

 is now accomplished, and further development begins. The 

 fertilized ovum divides, and so does also the so-called segmen- 

 tation nucleus, which owes its origin to the fusion of the two 

 pronuclei. We see therefore that substances from the mater- 

 nal side and from the paternal side are employed for the act 

 of propagation. A new individual obtains its life from both 

 parents. In this case also the history is uninterrupted. 



W. H. Moenkhaus,^^ Professor in the University of 

 Indiana, has furnished us the most brilUant proof of the 

 accuracy of the assertion just made. He reared the hybrids 

 of two fishes, Menidia and Fundulus. The chromosomes of 

 Menidiaare noticeably smaller than those of Fundulus. In 

 the hybrids Moenkhaus discovered both forms of chromo- 

 somes appearing clearly at the time of cell division. This 

 extremely interesting case teaches us by direct observation 

 that living substance from both parents propagates itself in 

 the progeny in visible form. 



At the beginning of today's lecture we cited the Latin 

 saying "omne vivum ex vivo." It required the prolonged 

 researches of many investigators to reveal to us the ways 

 which living substance adopts in order to continue without a 

 break. The relations may be easily recognized in asexual 

 reproduction, but in the case of sexual reproduction we must 



