SYNGAMY AND SEX IN THE PROTOZOA 147 



nuclear substance; that, consequently, by a regulative process 

 which may primitively have followed the syngamic union, the 

 chromatin of the zygote was reduced to the normal quantity by 

 elimination of half of its mass ; and that from this hypothetical 

 primitive process of regulation of the nucleo-cytoplasmic balance 

 a process of nuclear reduction preceding the syngamic act has been 

 gradually evolved until it reaches its perfection in the form seen 

 in the Metazoa. On this view, it is to be expected that in Protista 

 a great diversity in the methods of nuclear reduction would occur, 

 from those of the roughest type to others highly elaborated and 

 perfected ; and this expectation certainly receives justification 

 from the data of observation. Hertwig (119), on the other hand, 

 compares the reducing divisions in the maturation of the gametes 

 to the so-called ' hunger-divisions ' in Infusoria, which exhibit 

 a great disproportion in the relative mass of nucleus and cytoplasm 

 as the result of starvation in artificial cultures ; in such forms the 

 body is smaller than in forms from a normal culture, but the nucleus 

 is not merely relatively, but absolutely, larger than that of 

 a normal form. The disturbance in the nucleo-cytoplasmic ratio 

 (see p. 70, supra) can, however, be regulated by reducing divisions 

 of the nucleus. On the ground of this comparison, Hertwig considers 

 that the maturative processes of the gametes are to be regarded as 

 the necessary consequences of antecedent events* in the life-history 

 as processes which in their turn bring about syngamy, and not 

 such as have the object of preparing the nuclei for fertilization. 



In order to give a more concrete idea of the processes of syngamy 

 and reduction in Protozoa, a few typical examples will now be 

 described, selected in order to illustrate the salient features of 

 these processes. The most convenient method of classification 

 of the examples chosen is to distinguish those cases in which cliro- 

 midia are present in addition to nuclei from those in which nuclei 

 alone are present. 



1. Syngamy and Reduction with Nuclei and Chromidia. In a 

 great many Sarcodina, especially those belonging to the orders 

 Amcebsea (p. 218) and Foraminifera (p. 231), chromidia may be 

 present in the gamete-forming individuals as a permanent con- 

 stituent of the body-structure. In such cases the chromidia 

 represent, wholly or in part, the generative chromatin, and give 

 rise, by formation of secondary nuclei, to the nuclei of the gametes. 

 As an example Arcella may be taken, the life-cycle of which is 

 described in a subsequent chapter. In this form two distinct 

 forms of syngamy have been described. 



* It is, of course, hardly necessary to point out that starvation is by no means 

 the only influence which can bring about a disturbance of the nucleo-cytoplasmic 

 equilibrium ; over-nutrition, for example, may have the same effect. 



