ON -THE DEVELOPMENT OF DERMATOBIA HOMINIS. 497 



is intermediate in size between those of this row and those of the large circles. Behind 

 the last complete circle, that of the seventh somite, only two very small hooks occur 

 in the mid-ventral line. 



3. Larva B. The second larva of my series from the human host, which is also 

 the largest of all three, measures 12.7 millimetres in length by 6.2 millimetres in breadth 

 at the fifth somite. Less than one-third the entire length, about 4 millimetres, falls 

 in the constricted portion. This larva (PL XXXV, Figs. 6, 7, 8) is the most con- 

 tracted of all, as the anterior somites are forcibly drawn in and the tip of the ultimate 

 somite barely projects beyond the penultimate, within which it is in large part con- 

 cealed. In consequence of this the segmentation is more distinct, but the armature 

 is difficult to determine and the terminal somites are so contracted that they can 

 hardly be studied at all. The slenderer posterior portion also manifests the contracted 

 condition in the numerous irregular but deeply marked transverse folds or constric- 

 tions which are conspicuous throughout its entire aspect. 



On the dorsal surface of this larva (Fig. 6) one finds in the median line a row of 

 peculiar structures which are modifications of the general chitinous covering. They 

 are ellipsoidal in form, with the major axis transverse to the length of the body, and 

 are in general clearly marked off from the surrounding surface although the exact 

 line of demarcation is not sharp. From the furrow which limits them they rise as 

 low oval bosses, more transparent in character than the rest of the external surface. 

 The rows of hooks turn slightly forward or backward to pass around these areas, on 

 which no hook nor irregularity of the surface occurs. Their size is somewhat variable, 

 but this as well as their location is clearly given in the figure, which also shows their 

 remarkable transparency in that a partial row of hooks in the furrow between the 

 second and third somite may be faintly seen through one of these structures. They 

 occur, one on each somite from the second to the seventh inclusive. All are single, 

 but a faint shadow as of a coming line of division separates one into anterior and 

 posterior halves. The cuticula on these bosses is extremely delicate, for in the specimen 

 at hand it was accidentally punctured by a light touch from a dissecting-needle. 



Somewhat similar mammiform projections which appear to be just forming 

 are also evident on the somites elsewhere. They are not regular in outline, definite 

 in location, or smooth in surface like those just described, nor is their cuticula of the 

 same delicate character. Whether they are the beginnings of the bosses described 

 by Blanchard and others for later stages of the animal I must leave undecided. The 

 median ovals are, however, unquestionably the structures which these authors have 

 found heavily chitinized in later development. The other important external struc- 

 tural features are given in the following description. 



