ON THE DEVELOPMENT OF DERMATOBIA HOMINIS. 499 



becomes more crowded on the dorso-lateral f ace of the somite. These denticles are 

 of the same size as those on the preceding somite. In the incomplete circle of large 

 hooks which is situated near the posterior margin of this somite there are twenty-seven 

 hooks, fourteen on the right and thirteen on the left side. These hooks measure 

 330 to 390 micra in length by 210 to 240 micra in diameter at the base. It is thus 

 noticeable that while these hooks are actually larger than the corresponding hooks 

 of the preceding stage they have lost their conspicuous character since the smaller 

 hooks have increased in size far more strikingly. Thus it is that the large hooks no 

 longer contrast so strikingly with the smaller ones, and with the size of the body and 

 somites. One notes also that the rows are less symmetrically placed and the hooks 

 less uniform in size. On the dorsal surface a supplemental row of two hooks of good 

 size on either side lies just behind the incomplete row. These hooks are pointed not 

 backward but forward; that is, they are in anteversion. 



Somite V. The row on the anterior margin of the somite, which corresponds 

 to the first complete circle of large hooks in the preceding stage, contains here twenty- 

 seven hooks on the left half of the body and twenty-four on the right. This row is 

 not so regular nor are the individual hooks so uniform in size as in the preceding ones. 

 In general, these hooks conform in size to the measurements given for the hooks of 

 the preceding incomplete series, but smaller hooks, measuring only 240 to 300 micra 

 in length by 150 to 180 micra in diameter at the base, are intercalated at irregular 

 intervals. A parallel row of distinctly smaller hooks lies immediately posterior to 

 the series just mentioned. It contains nineteen hooks on the right and twenty-one 

 on the left and is complete only on the ventral surface. The lateral and dorsal aspects 

 •>how it to be much interrupted. The incomplete row near the posterior margin of 

 this somite contains fourteen hooks on the left and sixteen on the right and has a 

 supplementary dorsal row of ten hooks just posterior and parallel to it. This supple- 

 mental row has the hooks pointed forward. 



Somite VI. The anterior complete circle consists of twenty-three hooks on each 

 side of the body. The same irregularity which characterized the corresponding row 

 of the somite just described may be noted here also, and the hooks are of about the 

 same size, although a few exceptionally large ones measure 420 to 450 micra in length. 

 The parallel row of smaller hooks just posterior is present here also, but it is continuous 

 only on the ventral surface and occurs in patches elsewhere. The posterior incom- 

 plete series of this somite contains fifteen hooks on the right side and thirteen on the 

 left; it is interrupted on the mid-dorsal line and is supplemented by a short series of 

 smaller hooks posterior to this gap and extending laterally a short distance beyond it. 

 The contraction of the body and the consequent involution at the limit of the somite 



