492 ON THE DEVELOPMENT OF^ DERMATOBIA HOMINIS. 



margin of the band is very definite and^marked by a range of hooks noticeably larger 

 than the general run of those in the band. Dorsally the anterior hooks of the band 

 are also a little larger than those proximately posterior to them. 



Somite IV. The individual hooks here are again a little larger than those on the 

 preceding somite, as they measure 50 to 65 micra in length and 30 to 35 micra in 

 diameter at the base, though numerous smaller hooks occur irregularly among the 

 number. The band is somewhat narrower than on the last somite, since it covers 

 only two-thirds or less of the somite width. In one respect its appearance is notice- 

 ably modified; the anterior margin is marked by a line of hooks which though not 

 uniform include the largest of the band and are at least twice the size of those which 

 stand next to them. They suggest in a striking manner the conditions of the next 

 somite. The hooks on the lateral aspect are also larger on the average than those 

 which fill the ventral region of the band, though one does not find them more numer- 

 ous in the former region than in the latter. In a small area on the mid-dorsal line 

 the hooks extend further caudad than on the lateral or ventral aspects of the somite. 



In one respect this somite presents a radically new condition. Near the posterior 

 margin is found an incomplete circular row of hooks, much larger than any hereto- 

 fore noted. They measure 130 to 140 micra in diameter at the base and 180 to 200 

 micra in length, and point uniformly caudad. The series begins on either side about 

 60° from the mid-ventral line and extends in a single row around the dorsum. It con- 

 tains nine hooks on the right and the same number on the left side. Near the mid- 

 dorsal line are intercalated two small hooks. 



Somite V. A complete circle of large hooks, similar in form and size to those 

 in the posterior row of the last somite, marks here the anterior margin. The single 

 hook in the mid-ventral line is of only half size; posterior to it stands a pair of the 

 same size and around these are grouped five small hooks on the right and eight on the 

 left in an irregular supplementary row. In the main row there are six large hooks 

 on either side of the median line and before the incomplete row begins, and from that 

 point there are eight hooks on the right side and nine on the left, making a total of 

 twenty-nine in the entire circle. 



Along the dorsum this row is supplemented by a row of small hooks just posterior 

 and parallel to it, which contains five hooks on the right and seven of the same size 

 on the left, together with two very small hooks. 



The incomplete row on the posterior margin of the somite is present here also. 

 Its hooks correspond roughly to those of the preceding and succeeding series of large 

 hooks. This is most evident in lateral aspect where the antero-posterior ranges may 

 be traced entirely through the six circular series with exceptional breaks only. The 



