"Polarity:* 505 



ejected from the cell, leaving the cytoplasm behind? Assuredly 

 not! A small part of the cytoplasm goes into the tail of the sper- 

 matozoon, and since, in some cases, the tail is said not to enter the 

 egg that part of the cytoplasm is lost. The rest of the cytoplasm — 

 by far the largest amount in many cases ^ — concentrates around 

 the nucleus, enters the egg with it, and, no doubt, mingles with 

 the cytoplasm of the egg. It is a matter of common observation 

 that the chromatin of the nucleus must also greatly contract to be 

 stowed away in the minute sperm-head. If we compare the size 

 of the nucleus of the sperm mother-cell with the size of the head 

 of the spermatozoon the enormous difference in volume between 

 the two becomes apparent. It is true that most of the volume 

 of the nucleus consists of nuclear sap rather than chromatin, but 

 there can be no doubt that the chromatin itself may expand and 

 shrink within very wide limits. Have we not laid too much em- 

 phasis on the nucleus of the sperm-head because we can trace its 

 history with great clearness, and have we not ignored the cytoplasm 

 that is carried in, because becoming at once commingled with 

 that of the egg it is lost to sight? May it not be true that the 

 paternal cytoplasm becomes incorporated in the fertilized egg 

 as a part of the cytoplasm and as it increases in volume comes to 

 play its part in the differentiation of the cell. The accumulation 

 of cytoplasm around the male-nucleus^ which accompanies the 

 latter as it moves toward the female nucleus, its division and its 

 distribution to the daughter-cells suggests how the mechanism 

 of transmission may be accomplished. From this point of view 

 the protoplasm and not the nucleus might transmit the hereditary 

 qualities of the male as well as of the female. The nucleus would 

 be concerned with the metabolism of the cell. The more diffi- 

 cult question still remains, of course, as to how far the metabolic 

 influence of the nucleus might influence the cytoplasm and affect 

 its hereditary properties, but a discussion of this possibility in the 

 absence of data would be too speculative to be profitable. 



In conclusion we find that the localization in the cytoplasm of 

 the egg is directly comparable to the localization of the materials 

 of the adult animal. The *' polarity" in both cases is an expression 

 of the gradation in the material. The phenomena of regeneration 



'Its more watery parts are thrown off. 



^Generally supposed to come mainly from the egg, but which may also in part come from the sperm. 



