from this theory we arrive at an intelligible reason why the 

 offspring comes to resemble both parents but there are diffi- 

 culties ni the way of further tracing heredity which wo have 

 not time here to consider. 



Weismann's Theory.— Weismann's view is wholly different. 

 He distinguishes in the ovum two kinds of plasm, the germ 

 plasm and the histogenetic or ovogenetic nucleoplasm. The 

 germ plasm which is at first present in the young egg he con- 

 cludes originates first of all a special histogenetic or ovogenetic 

 nucleoplasm which controls the egg cell up to the point of 

 maturity, enabling it to secrete food material, develop mem-, 

 Cranes, etc. At maturity this ovogenetic nucleoplasm is of no 

 more use and incapable of retransformation into germ plasm, 

 and is hence thrown off by nuclear division forming the first 

 polar globule. This is all that is extruded in the partheno- 

 genetic ova. The second kind, — his germ plasm, — present in 

 the egg, is that which enables the ovum to develop into an em- 

 bryo. The second extrusion of a polar globule is a reduction of 

 this germ plasm of the nucleus by half and the same must occur 

 in the male germ cell also. What is thus lost in the forma- 

 tion of the second polar globule, is supplied by the fertilizing 

 spermatozoon. The beginning of development depends, accord- 

 ing to this hypothesis, upon the presence of a definite quantity 

 of germ plasm. This the normal egg attains by first losing 

 half and then regaining it ; while the parthenogenetic egg 

 attains the same result by never losing any. According to 

 Weismann's view we see that only the second polar globule has 

 to do directly with reproduction and here we have to look for 

 an explanation of reproduction and heredity. As mentioned 

 above Weismann looks upon the second polar globule, by 

 which the germ plasm is reduced one half, as a reduction not 

 only in quantity but above all in complexity of constitution, for 

 by this means, he reasons, the excessive accumulations of differ- 

 ent kinds of hereditary tendencies or germ plasms is prevented, 

 which without it would necessarily be produced by fertiliza- 

 tion. With the nucleus of the second polar body as many 

 different kinds of germ plasms are removed from the egg as 

 Will be afterward added through the sperm nucleus. This 



