498 ON THE DEVELOPMENT OF DERMATOBIA HOMINIS. 



Somite I. The two lateral mammiform protuberances (PI. XXXV, Fig. 10), 

 which may be regarded as rudimentary antennse, are much more distinct than in the 

 earlier stage. Each of these bears two clearly marked annular pigment spots near 

 its tip. The two hooks which project their tips from the dorsal wall of the mouth 

 are longer and much less sharply curved than in the earlier stage, although they are 

 both somewhat more flexed and notably more pointed than in the unformed condition 

 shown in the transforming larva (PI. XXXVI, Fig. 15). Neither on the ventral por- 

 tion of this somite which forms a distinct lip, nor on the dorsal which projects like a 

 broad undivided forehead, have I been able to detect a trace of the minute denticles 

 that formed conspicuous cheek and chin patches in the earlier stage of development. 

 The external surface of the first somite is apparently entirely unarmed. But on the 

 ventral wall of the infundibuliform oral cavity one can distinguish with difficulty a 

 few small denticles. It was impossible to make out their arrangement or to ascertain 

 definitely their number. Although a little larger than those described in the same 

 region in the previous stage of development, they are apparently not so numerous, 

 and the difficulty of demonstrating their presence would cause them to be overlooked 

 in most cases. 



The first somite was considerably retracted and it was impossible to see the stig- 

 mata figured by Blanchard ('92, p. 141, Fig. lie) on the lateral face and nearly in 

 the groove. A pair of large respiratory sacs lie within the body extending back to 

 the third and fourth somites; these may open here, though no connection could be 

 found nor even an indication of one. 



Somite II. Only about one-third of the surface of this somite was exposed. 

 One could distinguish three small teeth near the mid-ventral line and two groups of 

 seven to nine teeth each in the dorso-lateral groove. These teeth measure 120 micra 

 in length by 90 micra in diameter at the base. 



Somite III. The denticles were much more numerous than on the preceding 

 somite, being about seventy in all. They were arranged in a single row in the ventral 

 region and in two or three rows on the dorso-lateral surface where the denticles are 

 largest. A few are also seen in a single row in the dorsal groove. The denticles of 

 this somite vary in size as compared with those on the preceding somite and may 

 measure as much as 210 micra in length by 150 micra in diameter at the base; the 

 average size is 180 micra in length by 120 micra in basal diameter. 



Somite IV. Here a complete band encircles the anterior margin of the somite 

 with the exception of a short distance on the dorsal surface. There are about seventy 

 denticles in all, and these are arranged in an irregular double row which is somewhat 

 open and broken, forming in part only a single series on the ventral surface, but which 



