306 Dynamic Theory. 



through the reactions of the sexual gland, by which agency it is drawn 

 about nuclei and aggregated into functional cells. These nuclei, both 

 in the case of the male and the female elements, assimilate nutriment, in- 

 crease in size, and then divide, as is the usual mode of increase among 

 elementary organisms, not always equally, however, nor completely, nor 

 after the same fashion. 



FIG. 129. 



FIG. 129. Diagram, of Development of Reproductive Elements. 



1. An Amoeboid Sex-cell which may 5, 6, 7. Sperm Cell undergoing segmen- 

 give rise to either or both male and female tatioii into spores, 

 cells. s. Mature Spermatozoa approaching 



2. Ovum with, nucleus ( d ). Ovum ( 8 ). 



3. Ovum extruding first Polar body (a). 9. Male and Female nuclei c. d. ap- 



4. Ovum extruding second Polar body preaching each other. 

 (6). ( Geddes & Thomson. ) 



Division is especially conspicuous with the male elements, spermato- 

 zoa. But the behavior of the female elements, the ova, is in some cases 

 peculiar. Instead of the entire egg splitting into two equal halves, the 

 nucleus only divides equally, but one-half retains the whole or nearly 

 the whole of the substance of the egg, while the other half, with a very 

 small accompaniment of protoplasm around it, separates, or is "ex- 

 truded " from the more bulky part. This process is called the "extru- 

 sion of the polar globule. " " Polar globule " is correct, but we are not 

 to suppose that this one is any more polar than the half nucleus left be- 

 hind. Soon after this first extrusion, in most cases, a second one oc- 

 curs, the nucleus in the ovum dividing again and sending off polar body 

 No. 2. These divisions reduce the nucleus of the ovum to one-fourth its 

 original size. These extruded nuclei frequently hang around the out- 

 skirts of the ovum, and it sometimes happens that they divide, and oc- 

 cassionally they are joined by a spermatozoon in a union which of course 

 does not result in any further growth. It is evident that this division 

 of the ovum is the equivalent of the usual division of elementary cells, 

 and that the extruded globules are as female as the nucleus which re- 

 mains in the body of the ovum and differ from it only in their poverty 

 of equipment in the way of nutritive protoplasm. The difference in 

 general between the male and female germ cell appears to be that the for- 

 mer is holoblastic, or nearty so, while the latter is meroblastic. ( See 

 page 29. ) The male cell undergoes segmentation until it is all turned 

 into spermatozoa, each with a small bit of accompanying protoplasm, 



