187] LIFE HISTORY OF GORDIUS AND PARAGORDIUS—MA Y 67 



bodies disappear in the later stages and the intestinal wall in that region 

 becomes built up of large cells. In Paragordius varius I have found no trace 

 of the disappearance of the bodies in larvae that had lived in the free con- 

 dition for a long time. 



Schepotieflf in his description says that the bodies are formed from a 

 vesicle which arises from the dorsal side of the intestine. He states that 

 they are vesicles composed of walls filled with a gelatinous, feebly staining, 

 homogeneous mass. Each wall he believes to contain two flattened nuclei. 

 He thought this structure was similar to that of the reproductive tubes of 

 the adults. The present investigation, however, has revealed that the 

 gonads in the early stages are composed of cells of an undifferentiated 

 nature and consequently it is doubtful that they are derived from larval 

 structure of such specialized character. 



The reproductive organs in the two sexes arise in the same manner and 

 are differentiated only later in development. The term germinal epithe- 

 lium is hardly applicable to the early rudiments of the gonads. Even in 

 later stages, with the exception of the efferent ducts, no part of the repro- 

 ductive columns contains a structure that in any way resembles epithelium. 

 The resemblance of the walls of the oviducts and sperm ducts to epithelium 

 has been described by others. Rauther assumed from analogy with similar 

 structures in other animals that the gonads in this group must arise as 

 evaginations of some epithelial structure, and believed that the epithelial 

 remnants presented by the oviducts indicated that the evagination had 

 taken place at the point where the oviducts enter the cloaca. The results 

 of the present investigation show that this theory does not hold. The 

 gonads appear some time before there is any trace of an evagination in the 

 region that later forms the cloaca. The connection between gonads and 

 intestine is only secondarily acquired. Moreover, the epithelial structure 

 of the oviducts is not a remnant of a previous epithelial covering of the 

 gonads, but a secondary structure formed by the rearrangement of cells 

 that in the early stages show no indication of an epithelial nature. It is 

 possible, of course, that the gonads do arise from the posterior end of the 

 intestine, but in that case they are at first completely cut off, their origin 

 being more like that of mesenchyme than of mesothelium, and are later 

 reunited. 



In later stages the ovaries are still essentially like the testes, except that 

 the lower walls have become distended at intervals to allow for the growth 

 of the ova. The entire ovarian contents are transformed into germ cells 

 and consequently the membranes containing them have usually been 

 regarded as egg reservoirs or uteri. Even Montgomery, who was aware of 

 the true nature of the dorsal tubes, retained the name uterus for them. 

 He believed that the eggs at the time of laying pass back into those tubes 

 and backward along them to the oviducts. That, however, is an error. In 



