130 



GENERAL BIOLOC.Y 



cells are somatic and nutritive, while others are germ-cells or reproduc- 

 tive. Here also we come in contact with our first and lowest form of sex 

 life. Any organ which produces sex cells is known as a gonad. There are 

 certain germ, cells in a colony of volvox called parthenogonadia 

 ( - ). These divide into many cells which drop into 



the center of the mother colony and finally escape through a break in 



the wall. There are other germ cells, 

 however, which are also produced; the 

 smaller are called spermatazoa or 

 microgametes. These are the male 

 germ cells, while the larger ones called 

 macrogametes or eggs are the female 

 germ cells. The eggs are fertilized by 

 the spermatazoa, and, after passing 

 through a resting stage, develop into 

 new colonies. 



Colonies may be of one sex only. 

 In such cases the male colonies can be 

 recognized by the sperm pockets ar- 

 ranged in a wide belt around the mid- 

 dle of the colony with the poles free 

 from cells. 



There is a distinct difference in a 

 colony of single-celled animals of this 

 kind and a tissue which is a sheet of 

 similar functioning cells ; such sheet 

 being combined with others to form an organ while the organs form a 

 complete single individual. In Volvox there is no such grouping of 

 sheets of similar functioning cells. Each cell is complete and distinct 

 in itself and is as much an individual as Amoeba or Euglena just studied, 

 except that it is attached to its fello\vs. 



PLASMODIUM MALARIAE 



*'" The malarial organism, "Plasmodium malariae (Fig. 50), a member 

 of the class Sporozoa, nearly all of which are parasitic, lives in the hu- 

 man body. Human blood contains minute circular disks known as red 

 blood corpuscles, within which the malarial organisms may be found 

 in persons who are suffering from malaria, or chills and fever. The or- 

 ganism first appears as an extremely minute body, in shape somewhat 

 like the Amoeba, though much smaller. It increases in size. After 

 reaching a size which nearly fills up the red blood corpuscles, it breaks 

 up into twelve to sixteen small spores. The blood corpuscles now break 

 into pieces and the spores are liberated into the liquid blood. Each 

 may then make its way into a corpuscle and repeat again the history as 

 already described. 



Fig. 49. Volvox. 



The individual cells are united by radi- 

 ating strands of protoplasm. A, a mature 

 cdlony ; a. spermaries ; g, ovaries. B, zy- 

 gote resulting from the fusion of the 

 gametes. C, two sperm. D, egg. (From 

 West, after Klein.) 



