178 OXYURIS-LARViE HATCHED IN THE HUJIAN STOMACH, 



the lateral vessels constituted a fundamental part of the lateral 

 fields, the latter coming therefore to be regarded as perhaps also 

 excretory in their function. 



Several facts have long since come to light which render this 

 position untenable. In the first place it was found that the 

 lateral vessels were not always present on both sides. The 

 number of species possessing but one lateral vessel has gradiially 

 increased until, in the important genus A s c a r i s at least, two 

 vessels can hardly be said to be the rule. When, however, only 

 one lateral field has a vessel connected with it the other lateral 

 field remains, except for the disappearance of the vessel, essen- 

 tially unaltered, something not to be expected if the connection 

 between vessel and field was in any way intimate. In the second 

 place submedian fields exist, hardly to_,be distinguished in structure 

 from the lateral fields, and in connection with these submedian 

 fields no vessels have ever been seen. In the third place the con- 

 nection between the vessels and the fields though in some cases 

 apparently intimate is in many cases manifestly slight. 



Still when it became gradually established through the researches 

 of Eberth, Bastian, Biitschli, Von Linstow and De Man that the 

 existence of a unicellular gland emptying through a ventral pore 

 was of very general occurrence among free-living Nematodes, so 

 firmly had the idea of lateral vessels in connection with lateral 

 fields taken hold that the homology of the newly discovered 

 unicellular organ with the long known lateral vessels was not 

 recognized and it remains to day very incompletely acknowledged. 

 The homology is I believe complete. Once set up a disconnec- 

 tion between the lateral fields and the lateral vessels and the 

 homology is much more easily recognized. Reasons for holding 

 the connection which does actually exist as of no great significance 

 have been enumerated above. This connection may have, nay 

 probably has, been brought about quite mechanically. The 

 Nematode worm from the beginning undulates its body in a 

 dorso-ventral plane and this movement is an important factor in 

 the development and position of the organs, and to it is probably 

 due the position of the long lateral vessels of the large parasitic 



