153] LIFE HISTORY OF GORDIUS AND PARAGORDIUS—MA Y 33 



thinner, low magnification shows the two adjacent layers of heavy fibers as 

 a single dark layer and between two such dark layers the thinner fibers as a 

 lighter layer, thus giving the cuticula the appearance of being composed 

 of ten to fifteen dark layers (Fig. 124). 



The adult cuticula, macerated in nitric acid and separated into thin 

 layers, shows clearly under low magnification the rhomboids formed by the 

 intersection of the coarser lines (Fig. 5) and under high magnification the 

 finer intersecting fibers (Fig. 4). The coarser lines enclosing the rhomboids 

 are due to a slight increase in the thickness of the fibers as well as in the 

 pigmentation. 



The bristles of the adult cuticula, when they first become evident, are 

 heavy radiating strands connecting the larval cuticula with the hypoderm 

 (Figs. 38, 40). At first they are thick and translucent, but later they 

 become shrunken and opaque, and it is impossible to trace them beneath 

 the first layer of the fibrous cuticula. At the time of moulting they 

 become detached from the larval cuticula and remain attached to the 

 surface of the adult cuticula. The bristles pass thru the granular layer 

 (Fig. 44) and consequently are not covered by the homogeneous cuticula 

 of the adult. 



The postcloacal ridge of the male is formed by elongated cells in the 

 hypoderm (Figs. 37, 60, 61) and appears as a thickening in the granular 

 layer. In the adult it appears to be continuous with the homogeneous 

 cuticula and on cross section has the appearance of a stout hook set upon a 

 projecting base of the fibrous cuticula and curved slightly backward and 

 inward (Fig. 98). 



Over the anterior end the fibrous cuticula develops in the normal way, 

 but is not so thick as elsewhere. Later the fibres become more closely 

 packed together, all granular substances disappear, and the cuticula under 

 the white area becomes nearly homogeneous and transparent. 



During the entire period of development the layers of the cuticula are 

 pure white. Pigmentation begins when the homogeneous layer underlying 

 the larval cuticula has already begun to disintegrate. Pigmentation begins 

 first in the dark ring behind the anterior white area. It next delineates the 

 dorsal and ventral bands, beginning at the anterior end and passing back- 

 ward. By the time these bands are shown on about the anterior fourth 

 of the body, pigmentation of the rest of the cuticula begins at the anterior 

 end and slightly later also at the posterior end. At this end also the dark 

 bands appear first, but are never so clearly outlined as at the anterior end. 

 The bands from the two ends soon come together slightly posterior to the 

 middle of the body and the pigmentation of the rest of the cuticula pro- 

 ceeds in the same order. In case of all specimens observed leaving their 

 hosts the pigmentation could not be distinguished from that of free living 

 specimens. If specimens in which the pigmentation is not complete are 



