157] LIFE HISTORY OF GORDIUS AND PARAGORDIUS—MA 7 37 



the cord with fibres passing into the musculature and the hypoderm 

 surrounding the cloacal aperture. 



Peripheral nervous system. The ordinary methods of technic show 

 very little of the peripheral nervous system and consequently it will 

 have to be dismissed at this time with a few passing remarks. In a few 

 adults stained with iron hematoxylin nerve fibres were shown passing from 

 the nerve cord into the hypoderm and could also be traced for some dis- 

 tance in the hypoderm (Figs. 115, 118, 120). The fibres pass directly into 

 the hypoderm and, some distance from the cord, are seen to lie well within 

 the hypoderm mesad from the nuclei. At the time of the formation of the 

 cuticula it is u^ally possible to detect flask-shaped cells in the inner part 

 of the h5^oderm (Figs. 42, 129) and in a few cases fibres passing outward 

 from these cells or parallel to the surface of the hypoderm. 



Digestive system. The digestive system consists only of a straight tube 

 beginning near the anterior end and opening at the posterior end. Neither 

 mouth nor esophagus is present in this species at any stage of development. 

 The structures that might be mistaken for mouth and esophagus have al- 

 ready, in the discussion of the brain, been shown to be merely the spaces 

 previously occupied by parts of the larval proboscis. 



As in the larva (Fig. 20) so in the young parasitic forms, the anterior 

 part of the intestine consists of a solid mass of cells (Figs. 11, 15), and the 

 lumen begins behind this cell mass. Later this cell mass disinte- 

 grates, as is shown in some specimens of the twelve day stage (Figs. 67, 68). 

 By the time the twenty-eight day stage has been reached the space left by 

 the disintegration of those cells has been filled by mesenchyme, thus the 

 brain and intestine have become distinctly separated and the lumen of the 

 intestine is closed by a single layer of cells. In some cases, however, the 

 mass of cells does not disintegrate completely until a much later stage is 

 reached (Fig. 73). In either case the mesenchyme cells soon invade the 

 region between the intestine and the brain, so that in the later stages the 

 two come to be separated by a solid mass of parenchyma equal in length to 

 more than half the diameter of the body (Fig. 74). 



Whether or not there is in the larva and young parasite an outlet of the 

 cell mass thru the proboscis, can not be determined from the material at 

 hand. A tube can be traced from the anterior end to the base of the stylets 

 (Fig. 47) and in some cases appears to be indicated in the connecting 

 strand behind the stylets, but on account of the extreme minuteness of 

 the structures as compared with the thickness of the sections it is impossible 

 to make a definite determination. But, even if there is a tube leading 

 from the end of the stylets to the cell mass, it never passes thru the cell 

 mass to the lumen of the intestine. 



From the early stages until the adult cuticula has been nearly completed 

 the walls of the intestine consist of a syncytium of heavy cells with large 



