32 GEORGE T. HARGITT 



tinuity of the germ plasm. This seems to apply to many phyla, 

 even to vertebrates, but is especially marked in the coelenterates. 

 There are so many facts which contradict this theory that it may 

 confidently be held not to apply in the coelenterates, at any 

 rate. 



IV. GROWTH OF EGG CELLS 



1. Cytoplasmic growth 



The growth of egg cells proceeds by several methods in animals ; 

 nourishment is obtained either without assistance from other 

 cells, or else follicle cells, nurse cells, or other accessory structures 

 assist in securing or preparing the nourishment for the egg. In 

 none of the coelenterates is a follicle present nor are there nurse 

 cells such as occur in insects. But there are two distinct methods 

 of growth; one in which the food is obtained directly from the 

 enteric cavity or from the adjoining cells, and the second in 

 which neighboring cells are actually absorbed or engulfed. Often 

 both methods may be employed. The cells which are absorbed 

 have sometimes been called nurse cells, but they do not function 

 in the way nurse cells do in other groups, since they are con- 

 sumed instead of preparing food. Hydra, Tubularia, Pennaria, 

 and Hybocodon are examples of those eggs which absorb neigh- 

 boring cells for food, and Campanularia, Clava, Hydractinia, and 

 Aurelia are examples of those which obtain food from the enteric 

 cavity. 



A different origin has been claimed for nurse cells and egg 

 cells in those animals whose eggs are so nourished, the germ cells 

 representing real reproductive cells while the nurse cells are 

 held to be tissue cells. The Hydrozoa show no such distinc- 

 tion, for all the oogonia of any ovary are alike in origin and 

 capable of becoming ova; the determination of which shall 

 grow and which serve as food is largely a matter of chance. 

 Even after growth has started, the surrounding cells are like them 

 until degeneration phenomena become apparent in the cells 

 undergoing absorption. One explanation for the initiation of 

 growth is the presence of certain bodies in the cytoplasm. 

 Schaxel ('10 a, '11 a) describes the growth of oocytes of Pelagia, 



