151] LIFE HISTORY OF GORDIUS AND PARAGORDIUS—MA 7 31 



Later development 



From the nine day stage (Fig. 15) the parasite passes over into a spiral 

 form and this soon straightens out into a loose spiral and finally a straight, 

 cylindrical form with rounded ends. The straight form is often reached in 

 twelve days. After that the parasites, tho usually coiled in the body of the 

 host, are straight when relaxed in salt solution. In this they differ from 

 parasitic Mermithidae which when relaxed, take the form of a helix. To 

 the 28 day stage and beyond, the parasites are so transparent that it 

 requires a dark background to see them. Later stages are white until the 

 adult color develops. 



Development takes place uniformly thruout the length of the body. 

 This is shown in the stage of development of the nerve cord in figurers 

 29 and 72, taken from the middle and posterior end of the same specimen 

 and in the development of the cuticula in figures 108 and 107 taken 

 respectively from the anterior end and posterior end of a male in which 

 the fibrous layer of the aduU cuticula was in the process of formation. 



In the following discussions the different tissues and organs will be 

 taken up separately and their development traced to the adult structure. 

 Comparisons with the results obtained by other authors will be taken up 

 in a separate division of this report after the description of the different 

 structures has been completed. 



Cuticula. Earlier stages are covered only by the larval cuticula since 

 the adult cuticula appears very late in development. 



Larval cuticula. With the initiation of development there comes 

 a decided increase in the permeability of the cuticula. While it is almost 

 impossible to dehydrate and mount free living larvae without having them 

 collapse, the early parasitic stages may be mounted with comparative ease. 

 Together with this increase in the permeability comes an increase in the 

 thickness of the cuticula. While in the larva and the very young form it 

 appears only as a very fine line when magnified 800 times, in the twelve day 

 stage it appears as a much heavier line at a magnification of only 500 times. 

 Actual measurements give values of about 0.35/* foi the larva, 0.55/i for the 

 five day stage, and 0.7 fi for the twelve day stage. This increase in thickness 

 continues at about the same rate until the time the nerve cord separates 

 from the hypoderm and growth has already taken place in part of the germ 

 cells. At that time the diameter is nearly two micra. Soon after that there 

 appears directly beneath the cuticula a finely granular layer, stainable 

 with iron hematoxylin and alkaline methylene blue. There now appears 

 between the larval cuticula and the granular layer a more homogeneous 

 layer (Figs. 85, 112) not stainable in iron hematoxyhn (Figs. 108, 117) 

 but heavily stained by aniline blue in Mallory's connective tissue stain. 

 The larval cuticula remains connected with the granular layer by very 

 fine strands (Figs. 38). At times there appear in this layer larger 



