670 PATTERNS AND PROBLEMS OF DEVELOPMENT 



and nutritive cells. Other Hemiptera show somewhat similar relations: in 

 some, each of several oocytes is connected with a different nutritive cham- 

 ber apical to it, the strands from the more distant, older oocytes passing to 

 one side of those farther apical and younger. 



In the beetle Dytiscus four successive divisions of an ovarian cell pro- 

 duce sixteen cells, the basal, larger cell becoming the oocyte, the others 

 the nutritive cells. The nuclear content of the primary oogonium sepa- 

 rates into two visibly different portions preceding the first of the four divi- 

 sions. From one of these chromosomes form; the other passes entire into 

 the larger cell of the first division, and in each successive division it passes 

 into one cell, finally forming a large ring in the nucleus of the oocyte. This 

 has been regarded as a kind of diminution of chromatin in the nutritive 

 cells, analogous to that in Ascaris. A similar "diminution" has been de- 

 scribed for certain other insects.'' 



In Figure 218, Z), an oocyte of Dytiscus is shown with the intranuclear 

 ring and seven of the fifteen nutritive cells, all cytoplasmically continu- 

 ous. What Nusbaum-Hilarowicz (19 18) regards as streams of mitochon- 

 dria passing from the nutritive cells to the oocyte are indicated in the 

 figure. 



The apical region of the ovarian tubule of the queen bee contains small 

 cells, all apparently alike; lower in the tubule the oocytes, apparently ir- 

 regularly distributed, become distinguishable by their larger size (Fig. 

 2 1 8, £) . With progress down the tubule they gradually become more regu- 

 larly arranged along the tubule axis and spaced at more regular intervals 

 with the small cells between them. At a still later stage each oocyte is 

 associated with, and extends into, a group of nutritive cells apical to it 

 (Fig. 218, F). A follicle develops about this complex, forming a thick 

 columnar epithelium about the oocyte, thinner about the nutritive cells 

 (Paulcke, 1901). 



The polarity of the insect egg coincides in direction with the axis of 

 the ovarian tubule, the apical pole being directed toward the apical end 

 of the tubule. When nutritive cells are present, the oocyte is usually as- 

 sociated with a cell or group apical to it, that is, nutritive material from 

 these cells enters through that part which becomes the apical pole. In the 

 Crustacea, however, cells basal, as well as apical, to an oocyte function as 

 its nutritive cells. If the cells are all alike primarily — all potentially 



^''Dytiscus: Giardina, 1901; Debaisieux, 1909; Nusbaum-Hilarowicz, 1918. Gryllus: 

 Buchner, 1909. Colymbetes (Coleoptera) : Gunthert, 1910. See also E. B. Wilson, 1925, 

 p. 326. 



