500 ON THE DEVELOPMENT OF DERMATOBIA HOMINIS. 



makes this series of hooks appear to run into the anterior row of the succeeding somite 

 when the body is viewed dorsally. The hooks of this small supplemental row point 

 forward. 



Somite VII. The anterior row of this somite appears even more irregular than 

 those already mentioned. Its composition cannot be accurately ascertained on account 

 of the infolded margin of the somite as already noted, but there are about twenty 

 hooks on either side of the body. A scattered row parallel to the main series and 

 posterior to it occurs on the ventral surface and is represented by isolated hooks or 

 small groups on the sides and dorsum. The hooks vary in size here as on the preceding 

 somites. It seems as if the posterior margin of this somite were marked out by a 

 furrow separating it from the unsegmented contracted portion of the body; such a 

 limit was not present in the earlier stage. There is also a suggestion of further seg- 

 mentation in that among the transverse folds of the constricted portion which follows 

 this somite there are two or three regions deep enough to represent the limit of suc- 

 cessive somites. I am, however, entirely unable to find any further evidence of seg- 

 mentation in this region than the indistinct indication just noted. 



Somite XI. This somite is almost entirely contracted within the tenth somite, 

 as there appears beyond the collar of the latter only an irregular narrow rim of hooks. 

 The smooth part has entirely disappeared and by retractor muscles attached to the 

 inner surface of the face the convex tip has been withdrawn so as to form an irregular 

 hollow (PL XXXV, Fig. 9). This represents the maximum of contraction and agrees 

 with some figures of the larva previously given. Evidently it shows nothing of the 

 true form of the somite, and of internal structures one can distinguish only the dis- 

 torted sacs into which the stigmata open. 



In general one may say of this larva that the differences between the large and 

 small hooks are by no means so marked as in the preceding stage. The rows of large 

 hooks are not so regular in position and size and the armature of the larva has in 

 general a more confused aspect. The dorsal ovals are a conspicuous and characteristic 

 feature, which appears for the first time at this stage. 



Three short supplemental rows, those just posterior to the incomplete series on 

 the fourth, fifth, and sixth somites, are new formations at this stage and are com- 

 posed of hooks directed forward (in anteversion Blanchard). The meaning of these 

 structures is doubtless to be found in the migration of the larva, which occurs at the 

 end of this stage of development. 



Again it may be said that this larva agrees in all essential details with that 

 described by Blanchard ('92, p. 140) under the name of torcel. Its noticeably lesser 

 length is certainly due to excessive contraction. The hooks in this specimen are 



