ON THE DEVELOPMENT OF DERMATOBIA HOMINIS. 503 



On the new skin the hooks which replace those already described are much less 

 numerous. They stand in an irregular row near the anterior margin of the somite, 

 and are most abundant on the lateral and dorsal aspects where the row is often double 

 or triple. Though fewer, they are, however, much larger than the old hooks of this 

 somite, as they measure 100 to 150 micra in length and 60 to 90 micra in diameter at 

 the base. Their smaller number in spite of greater size causes them to leave a much 

 larger portion of the surface of the somite uncovered. 



Somite IV. The band of small hooks on the outer skin covers less than the 

 anterior half of this somite. Here the hooks stand in several indistinct rows, of which 

 the anterior is the most regular and also most prominent by virtue of the regularity 

 and size of the hooks, a feature most conspicuous in dorsal aspect. These hooks are 

 replaced by a few which are much larger, being from 150 to 210 micra in length and 

 90 to 120 micra in diameter at the base. The new hooks form an irregular double 

 row save in dorsal aspect where the series is single. They are most numerous in lateral 

 view. The contrast between old and new hooks is clearly illustrated by the camera 

 drawing (Fig. 17) of a small area from the lateral face of this somite. 



On this somite occurs the anterior incomplete row which contains on the outer 

 skin in this specimen ten hooks on the left side of the body and nine on the right. 

 These hooks measure 120 to 150 micra in basal diameter and 240 to 300 micra in length. 

 They are replaced by hooks on the inner skin which are slightly smaller and decidedly 

 more numerous; of new hooks there are sixteen (?) on the right side and eighteen 

 on the left. It is also noticeable that the new hooks are not so uniform in size or 

 regular in position as those of the old skin. The inner skin also bears a supplemental 

 row of four or five hooks which are distinctly directed forwards. 



Somite V. In the outer skin the anterior complete row consists of five hooks 

 on either side ventral to the incomplete row and eight hooks on either side parallel 

 to it, making twenty-six hooks in all. On the ventral surface there are one median 

 hook of half size and about fifteen others of minute size and irregular distribution. 

 On the ventral surface the five left hooks of the main row are replaced by eight new, 

 the five right by nine new, and the dorso-lateral eight are replaced by sixteen on the 

 left and fifteen (?) on the right, making about forty-eight in the entire circle. These 

 show the irregularity in size and position already noted. The subsidiary ventral row is 

 replaced by twenty-five to thirty hooks of half size, forming an irregular row parallel 

 to the main row in general and closely set in ventral aspect. Dorsally a group of 

 six replaces three minute hooks behind the main row on one side and other minute 

 hooks are not replaced at all. 



The half row on this somite comprises on the old skin eight hooks right and ten 



