GENERAL LAW OF ANIMAL FERTILITY. 595 



tli at the sperm-cell, which is supplied by tne male, contains co- 

 ordinating matter, and the germ-cell, which is supplied by the 

 female, contains matter to be co-ordinated. 



The same inference may, again, be drawn from a general view 

 of the maternal function. For if, as we see, it is the office of 

 the mother to afford milk to the infant, and during a previous 

 period to afford blood to the foetus, it becomes probable that 

 during a yet earlier stage it is still the function to supply nutri- 

 ment, though in another form. Indeed when, ascending gradually 

 the scale of animal life, we perceive that this supplying of milk, 

 and before that of blood, is simply continuation of the previous 

 process, we may be sure that, with Nature's usual consistency, 

 this process is essentially one from the beginning. 



Quite in harmony with this hypothesis concerning the respec- 

 tive natures of the sperm-cell and germ-cell is a remark of Car- 

 penter's on the same point: 



" Looking," he says, " to the very equal mode in which the characters of 

 the two parents are mingled in hybrid offspring, and to the certainty that the 

 material conditions which determine the development of the germ are almost 

 exclusively female, it would seem probable that the dynamical conditions 

 iu great part, furnished by the ma 



ly female, it would seem probable that the dynamical conditions are, 

 ,le." * 



12. Could nothing but the foregoing indirect evidence be 

 adduced in proof of the proposition that the spermatozoon is 

 essentially a neural element, and the ovum essentially a haemal 

 element, we should scarcely claim for it anything more than 

 plausibility. On finding, however, that this indirect evidence is 

 merely introductory to evidence of a quite direct nature, its 

 significance will become apparent. Adding to their weight 

 taken separately the force of their mutual confirmation, these 

 two series of proofs will be seen to give the hypothesis a high 

 degree of probability. The direct evidence now to be considered 

 is of several kinds. 



On referring to the description of the process of multiplication 

 in monads, quoted some pages back ( 5), from Professor Owen, 

 the reader will perceive that it is by the pellucid nucleus that the 

 growth and reproduction of these single-celled creatures are regu- 

 lated. The nucleus controls the circulation of the plasmatic 

 fluid ; the fission of the nucleus is the first step towards the 

 formation of another cell ; each half of the divided nucleus estab- 

 lishes round itself an independent current ; and, apparently, it is 

 by the repulsion of the nuclei that the separation into two indi- 



mitritive system greatly exceeds the other systems in development, the female 

 is commonly the largest, and often greatly so. In some of the Rotifera the 

 i;i:ile has no nutritive system at all. See Prin. of Phi/s.. p. 954 

 * Prin. ofPhys., p. 908. 



