Packard.] 366 [Jamiarj' 22, 



lobos in their (levelojmient are exact equivalents; there is an antero- 

 posterior symmetry very clearly shown. But in this stage (Fig. 1), 

 after the two ends of the body have been evolved from the prim- 

 itive cell-layer, development in the post-abdominal region is retarded, 

 that of the cephalic region progressing with much greater rapidity ; 

 thus the statement is true, that thenceforward the body develops 

 from before backwards. 



The development of the hinder, or post-oral, rings of the head, to- 

 gether with the antennal segment, i. e., the first one in front of the 

 mouth, accords at this time with that of the thoracic segments, so that 

 the process of development of the two regions and their appendages 

 is nearly identical. 



3. In the next stage (not figured) the yolk is completely walled in, 

 though no traces of segments appear on the dorsal and pleural areas. 

 The revolution of the embryo has taken place; the post-abdomen 

 being curved beneath the body. The eggs being oval, the change in po- 

 sition of the posterior end of the abdomen is not so well marked as in 

 eggs of a sj)herical shape, where the embryo has less room to develop. 

 This change of position may in part be accounted for by the increased 

 size of the median part of the abdomen, which thus pushes the head 

 (which meanwhile contracts) forward nearer the end of the egg, sa 

 as to allow the post-abdomen to slij) downwards and rest on the ven- 

 tral wall of the body. The yolk granules fill the entire cavity of the 

 body, extending into the appendages. The head has enlarged, the 

 remaining abdominal sternites appear, and the abdominal lobe, or 

 post-abdomen, is indicated, being curved under the body, and its end 

 touching the middle of the abdomen. 



The rudiments of the eyes appear as a darker, rounded mass of cells 

 indistinctly seen through the yolk-granules, and situated at the base 

 of the antenna?. They consist of a few epithelial cells of n-regular 

 tbrm, the central one being the largest. The three anterior append- 

 ages, when seen sideways, are equal in size and length, the antennse 

 being veiy contiguous to each other. 



The second maxilla; are a little over twice the length of the first 

 maxilla; and are grouped with the legs, being curved backwards. 

 They are, however, now one-third shorter than the anterior legs. 

 The second-maxillary sternum is still visible. 



The legs are now unequal in size, the two anterior pair being of 

 the same length, though the middle pair are slightly thicker than the 

 first pair; while the third, or posterior pair, are a third longer, and 

 drawn back upon the side of the body, the ends nearly reaching the 

 end of the egg. 



The tip of the abdomen (post-abdomen) consists of four seg- 



