ON THE DEVELOPMENT OF DERMATOBIA HOMINES. 501 



much more numerous than on Blanchard's, which came from Colombia, and the bosses 

 are less mature, for he speaks of them as more or less advanced in chitinization, whereas 

 these are very delicate. In one particular which I regard as important this descrip- 

 tion differs from that of Blanchard. This author speaks of the anterior girdle of hooks 

 on somites IV to VII as consisting of a double row of hooks, irregular in size and 

 arrangement. I have preferred to speak of the two rows separately because they 

 differ in size and in completeness, as already described ; and as will be demonstrated 

 later, they also differ in origin, for the anterior row corresponds to the single circle 

 of large hooks in the earlier larva, to which alone Blanchard applies the corresponding 

 term of girdle at that stage. So far as can be determined, the posterior region, though 

 somewhat corrugated, has no annulations. Whether they are obscured by con- 

 traction or are not yet definitely formed I must leave undecided. 



4. Larva C. The larva of intermediate size in my series (PL XXXVI, Figs. 11, 

 12, 13), the smaller of the two from the human subject, measured 12.8 millimetres in 

 length by 4 millimetres in breadth at the fifth annulus; of the length, 6.8 millimetres 

 fell in the anterior and 6 millimetres in the posterior region. It is also somewhat 

 curved ventrad, as Figure 12 shows. Like that first described it is well expanded and 

 at first sight is characterized only by a noticeable blackness and distinctness on the 

 part of the individual denticles. A closer examination of the specimen discloses the 

 important fact that it is about to molt, and the new skin with its armature already 

 perfect lies just beneath the old skin, so that careful study enables one to compare 

 with exactness corresponding regions on the two forms. In a few places opacity or 

 the interference of internal organs prevents an exact enumeration of the hooks, but 

 for the most part the specimen is fortunately transparent and hence easily studied. 

 Neither skin carries structures which can be properly designated as spines, for the 

 projections, even though minute as they are on the first three somites, are clearly 

 uncinate. In general, the size of these structures increases from the first to the fourth 

 somite, though the difference between those on the first and those on the second is 

 much greater relatively than in the other somites noted. The denticles on the outer 

 skin are uniformly so dark brown as to appear black and are very irregular in basal 

 outline, while those of the new skin are clear chestnut-brown and throughout symmet- 

 rical in outline, their bases being relatively smaller. On the old skin all denticles 

 are directed caudad or nearly so; on the new skin a few to be noted later are in ante- 

 version. A detailed description of the specimen may be given somite by somite. 



Somite I. The surface forms a low, rounded projection, looking obliquely ven- 

 trad, on which one cannot distinguish the antennary protuberances noted in the other 

 larvae. On the outer surface (Fig. 14) are distributed irregularly in oblique crescentic 



