184 THE EMBRYOLOGY OF THE HONEY BEE 



great increase in size of the oenocytes and fat cells between the 

 newly hatched larva and the larva four days old may be gained 

 by comparing figures 70 A and 75, Ocn, these two figures being 

 drawn at the same magnification. 



As in older larvae the oenocytes at Stage XV are principally 

 distinguished by their size which, although somewhat variable, is 

 only equalled by the neuroblasts and some of the blood cells. 

 Their form is largely determined by their location. When free 

 they are more or less spherical as in figure 70B ; when in close 

 contact with other cells, polyhedral, as in figure 70A. The nucleus 

 is usually more or less spherical and its chromatin content is in 

 young larvae not especially different from that of the cells of 

 other tissues. The cytoplasm presents a rather more homogen- 

 eous appearance than that of the fat cells. The oenocytes are 

 rather irregularly scattered throughout the body cavity and are 

 frequently enmeshed in the fat cells, as in figure 70B. At Stages 

 XIV and XV oenocytes are rare in the first three trunk seg- 

 ments, in other words the oenocytes during these stages are found 

 principally in the last twelve trunk segments, corresponding to 

 the imaginal abdominal segments of insects of other orders than 

 the Hymenoptera. 



In surface views of many embryos of Stage X small clear spots, 

 like those of the rudiments of the spiracles, may be seen to alter- 

 nate with the last eight spiracles of each side, so that the latter 

 have the appearance of being double. Transverse sections show 

 that there are actually at this stage pit-like invaginations of the 

 ectoderm precisely in line with the spiracles and that each of 

 these invaginations is situated half way between the adjacent 

 spiracles. 



Each pair of spiracles is, however, situated, not in the middle, 

 but in the anterior half of the corresponding segment, so that 

 each pair of the invaginations just described belongs to the pos- 

 terior half of the same segment as the pair of spiracles next in 

 front (cephalad of it). Accordingly these invaginations are 

 located on the third to the eleventh trunk segments, or, regarding 

 only the first three trunk segments as belonging to the thorax, 

 the first eight abdominal segments. These invaginations corre- 

 spond in form, size and location with the "metastigmatic" invagi- 



