M! ;''! ( ) H ; 

 1110 THE REPRODUCTIVE ORGANS 



by nt)thing more than the ordinary force of cohesion. Hence, if its 

 mass becomes too large, this force, ampHfied by adhesion, is no longer 

 sufficient to act throughout its substance, in spite of the fact that the 

 proportion of its surface to its mass becomes less as its size increases. 

 Moreover, since the processes of life are controlled by the nuclear 

 material and not by the cytoplasm, the mass of the latter must be 

 restricted, otherwise the nucleus cannot make its influence felt through- 

 out the cell. It is for this reason that those cells which must of 

 necessity attain a large size, such as the leukocytes and giant cells, 

 invariably embrace several isolated nuclei. To begin with, of course, 

 the growth of these simple protoplasmic units depends upon the fact 

 that their acquisition of new material exceeds the destruction. Even- 

 tually, however, when a limit in their size has been reached, their assimi- 

 lative power is gradually diminished. Even a division of their mass 

 may then result, but only if it is also in possession of a sufficient 

 amount of nuclear substance. When the latter is removed completely, 

 the cytoplasm cannot continue to exist for any length of time, because 

 it then lacks its 'Hrophic^^ factor. 



Contrary to growth, therefore, the process of reproduction 

 depends upon the formation of daughter-cells by the division of the 

 mother-cell; but it will be seen that these occurrences are not inde- 

 pendent of one another, because without activity and growth there can 

 be no reproduction. The manner in which this rejuvenation of living 

 matter is accomplished differs greatly in different animals. The 

 simplest procedure prevails in the unicellular organisms, because 

 these entities multiply by the asexual process of simple division or 

 amitosis. The mother-cell splits into two parts, each of which is 

 equipped with a certain amount of nuclear substance. In accordance 

 with Remak (1858), cell-division begins with a splitting of the nucleolus 

 which is then followed by a constriction and division of the nucleus, 

 cell-body and enveloping membrane. The daughter-cell so formed 

 grows and gradually acquires the characteristics of the mother-cell, but 

 only if it is subjected, to identical conditions. If not, its molecular and 

 general morphological character may be altered in such a manner that 

 it may give rise to an entirely new species. 



This amitotic manner of reproduction frequently gives rise to a 

 perfectly amazing multiplication. Thus, it has been stated that a 

 Paramecium, if it were plentifully supplied with food and protected 

 against injurious influences, would be able to form in the course of a year 

 a mass of living matter as large as the earth. If nothing more, this 

 computation gives us an idea regarding the perfectly phenomenal pos- 

 sibilities of this process. But, it is also true that amitosis cannot con- 

 tinue for an indefinite period of time and certainly not if the organisms 

 are forced to exist under unfavorable circumstances. It seems that 

 they then lose their vigor and become non-resistant so that they are 

 more easily affected by outside influences. Under these conditions, a 

 type of reproduction is frequently brought into play which is called 



