594 



THE AMERICAN NATURALIST. [Vol. XXXVII. 



Oogenesis. — Between the manubrium and the bell is a large 

 mass of cells, which as we have seen above, is derived from the 

 ectoderm and is destined to give rise to the future reproductive 

 elements. Brauer ('91, p. 575) in speaking of the origin of the 

 genital products in Tubularia mesembryantliemitin says, "Die 

 Geschlechtsprodukte von Tubularia entstehen aus interstitiellen 

 zellen des Ektoderms des Gonophorentragers, sie treten nahe der 

 Ursprungstiitte eines Gonophors ins Entoderm iiber, wandern 

 hier ihrer Reifungsstatte, dem ektodermalen Glockenkern, zu." 



Weismann ('83) states that in some hvdroids, the reproductive 

 elements may originate in the coenosarc of the trophosome. 

 While this is very rarely the case in hydroids where a definite 

 medusoid is developed, I have found one case where there 

 appeared to be a small egg cell in the ectoderm of the stem. 



female gonophores, 

 are a great deal 

 larger than those 

 of the surrounding 

 layers. They are 



gether, nearly 



i!n!mnlnnmcleoli. 

 (Fig. 11, a.) For 

 a time these cells 

 all increase slightly 



plasm in the mean- 

 time becoming 

 somewhat denser 

 from the periphery toward the center of the cell. At this stage 

 may generally be found four or five cells which are outstripping 

 their neighbors in growth and are attaining a considerably greater 



The cells of the germinal layer, especially in 



