100 INSECTS AFFECTING DOMESTIC ANIMALS. 
Second stage.—In the absence of any knowledge of an intermediate form, the larva 
found in the esophagus may be considered as the second stage (fig. 44). The indi- 
viduals vary in length from 11 to 1£ mm. and are quite smooth and devoid of prickles, 
except some minute ones, which appear like black specks partly : 
surrounding the anal spiracles (fig. 44, d) and a few extremely a 
minute ones just above the mouth parts (fig. 44, ¢). The former, 4 
or those around the anal spiracles, are of peculiar structure, 
and consist of a circular, brownish-black, slightly elevated 
base, in the center of which arises a short, stout, posteriorly 
curved very minute spine, less than one-half the diameter of 
the base in length. The mouth parts are more prominent than 
in the first stage, and the apical portion is broadened and fur- 
cate near the base (fig. 44, b, c). This stage does not differ in 
any essential way from the stage first found under the skin in 
the back before the perforation to the surface 1s made. (See 
fig. 45, a, b, c.) 
Fic. 44.— Hypoderma Third stage.—In this stage, which is the second form of the 
lineata: Secondstage larva found in the back (fig. 45, d, e, f), the larva again diverges 
of larva from cso- markedly from the second or preceding stage and acquires many 
phagus; a, larva; b, of the characteristics of the mature larva. It tapers, however, 
eee aes considerable toward the posterior extremity, rather than the 
Herne Satine reverse, and the spinous armature varies considerably in differ- 
d, enlargedend view ent specimens, but ventrally is similar to that of the adult, the 
of anal segment, spines being, however, morenumerous and less prominent. ‘The 
showing spiracles  Jateral armature is sometimes almost wanting, but occasionally 
and spines (from In- : : 
Seob Lite). occurs to the amount shown in the figure (fig. 45, d). The dor- 
sal armature is much more scanty, and is either limited to the 
first and second joints or frequently entirely wanting. 
Fourth stage.-—The fourth and last larval stage is shown with characteristic arma- 
ture at, fig. 45 g, i, dorsal and lateral views. Its chief difference from the larva of 
bovis (as shown in the diagram) is that the penultimate segment ventrally and also 
Sp RoR ROYER 
Nm cee *t O86 a cael ae 
mele 
i SRSA res 
NEE 
Fia. 45.— Hypoderma lineata: a, second stage of larva from back; b and ¢, enlargement of extremi- 
ties; d, ventral view of third stage, with details of extremities at e and /; g, dorsal view of mature 
larva, with enlargement of anal spiracles at h; 7 ditto, lateral view—natural size indicated by side 
lines (from Insect Life). 
dorsally is spinose, as the preceding ones on the posterior margin, while in bovis it is 
distinctly unarmed. The full-grown larva when escaping from the back is of a gray- 
ish-white color and ranges in length from 22 to 25 mm. 
