32 ILLINOIS BIOLOGICAL MONOGRAPHS [152 



amorphous bodies which are probably due to the action of the killing agent. 

 This homogeneous layer, as it may be called, attains a diameter of about 

 10/i at the time the tissues of the parasite have reached their full develop- 

 ment and then begins to disintegrate. By the disintegration of this 

 layer the larval cuticula becomes loosened from the underlying granular 

 layer (Fig. 39), soon becomes torn, and is sloughed off from the body 

 of the parasite when it is ready to leave the host. When fully developed 

 parasites are taken from their hosts pieces of the larval cuticula are 

 often seen trailing from one or both ends like transparent threads. The 

 larval proboscis which has been lying just beneath the larval cuticula 

 (Fig. 73) is also shed at this time. In some cases the deeper part of the 

 intervening layer does not become disintegrated by the time the larval 

 cuticula is shed and remains for a short time attached to the granular 

 layer, but ultimately it becomes entirely removed. The structure of the 

 larval cuticula is homogeneous thruout. 



Adult cuticula. The earliest beginning of the adult cuticula is the 

 formation of the granular layer under the larval cuticula as described in 

 the previous section. This granular layer, which increases somewhat in 

 thickness, but never has any very definite boundaries, forms the layer 

 known as the homogeneous cuticula of the adult. The granules become 

 crowded closer together so that they are not easily distinguishable. 



The fibrous cuticula of the adult appears as a differentiation of the 

 cytoplasm of the hypoderm some time after the formation of the granular 

 layer, when the intervening homogeneous layer has already reached nearly 

 half its final diameter (Figs. 112, 41, 35, 116). Thruout development the 

 fibrous cuticula consists of fibrous strands connecting the granular layer 

 with the hypoderm and of an intervening matrix (Fig. 43, 119). The 

 intervening matrix is under the most favorable conditions resolvable 

 into layers of fibers perpendicular to the radiating strands and forming 

 nodules at the intersections with those strands (Fig. 43). The fibers 

 composing these layers in the matrix are the rudiments of the ultimate 

 diagonally intersecting fibers of the adult cuticula. The nodules at first 

 appear to produce a thickening of the radiating fibers but later fuse 

 along the diagonal fibers and separate from each other along the radiat- 

 ing fibers to form the heavy fibers of the adult cuticula. The layers of 

 diagonal fibers are not formed in a regularly alternating series, but two 

 layers in one direction alternate with one in the other (Fig. 38). This fact 

 can be determined only on diagonal sections made parallel to the fibers of 

 one of the layers. The number of layers of intersecting fibers is variable, 

 but near the middle of the body it is about 45 (Fig. 38) and even on the 

 prongs of the fork of the male it is seldom less than 30 (Figs. 121-123). 

 Since in two adjacent layers of parallel fibers the fibers of one are of the same 

 diameter as those of the alternating layer, but those of the other are much 



