THE CAUSAL PARASITE. 31 



depth below the surface of the root of even 5 or more centimeters. 

 The latter has been observed by the writer in roots of sweet potato 

 (Ipomoea batatas) at Miami, Fla. 



Within the tissues the larva becomes fixed in position and remains 

 quiet except for occasional movements of the spear and esophageal 

 bulb. Whether all the nourishment is taken through the hollow 

 spear or some is absorbed directly through the skin was not deter- 

 mined. It seems probable, however, that the former is the case, 

 especially in view of the fact that the female occasionally bursts the 

 surrounding tissues of the root, so that she lies outside the latter 

 except for the anterior portion, which remains buried in the tissues. 



Growth begins almost immediately. This is mainly, however, in 

 thickness and only slightly in length (PI. I, figs. 5, 6, 7, and 8). By 

 the time a gain of 10 per cent in length has taken place the thiclaiess 

 has increased five to ten fold. This increase in thickness is confined 

 to the region anterior to the anal opening and in the main posterior 

 to the esophageal bulb. The alimentary canal posterior to the bulb 

 becomes greatly enlarged. In a week or ten days the larvae of both 

 sexes are spindle shaped. By the end of the fifteenth to twentieth 

 day the diameter is about a fourth of the length and the differentiation 

 of the sexes becomes apparent (PL I, figs. 9 and 13). According to 

 Stone and Smith ^ the female nematode slieds her skin four or five 

 times during the course of development, the first time just before 

 leaving the egg and the other two or three times before the final molt, 

 when she becomes sexually mature. The writer has been unable to 

 confirm this statement. In none of the specimens examined was any 

 sig-n of shedding the skin apparent on leaving the egg, although on 

 this point the evidence is slight, as special attention was not given to 

 it. On the other hand, no trace of old skins could be found sur- 

 rounding the developing larvae within the galls up to the time of dif- 

 ferentiation of the sexes. It seems possible that the investigators 

 referred to may have been misled by tlie fact that an injured nematode 

 sometimes secretes a new cuticle underneath the old or on account of 

 the circumstance that the molting may commence at one point long 

 before it is visible elsewhere. If these extra molts do actually occur 

 it seems strange that no signs are to be found of the cast-off skins 

 around the nematode. 



The ^\Titer's observations lead him to the following conclusions: 

 The sexes are alike (externally at least) up to about the fifteenth 

 day, or sometimes longer. Then a new skin becomes visible under- 

 neath the old, from wliich it becomes separated at various points. 

 In the female the most marked change is that of the shape of the 

 posterior end of the body, wlfich no longer ]:>ossesses the tail it had 



' stone and Smith, 1898, p. 22. 

 91294°— Bui. 217—11 3 



