NEMATODE GENUS PHYSALOPTEKA. 1009 



spicules. According to Seurat (1917 «), who has studied Ph. 

 leptosoma, this species has only two uteri, so that again it 

 appears that Travassos has made a new genus on wrong data. 

 At any rate the name Leptosoma is not available, as according to 

 Scudder (1882) it has already been used by Leach (1819) for a 

 beetle, by Risso (1826) for a crustacean, by Nardo (1827) for a 

 fish, and by Boisd. (1833) for a lepidopteran, while the form 

 Leptosomibs was used by Vieill. (1816) for a bird, and by Schonh. 

 (1826) for a coleopteran. 



With regards to the genera Thubttncecfj Seurat, 1914, Heli- 

 conema Trav., 1919, and Proleptus Duj., 1845, it does not 

 appear necessary to discuss them here, as they do not affect the 

 status of the genus Fhysaloptera. 



Seurat (1915-16) has also proposed dividing the genus into 

 four groups according to the teeth. These groups he characterises 

 briefly as follows : — • 



1st group of PTi. galinieri Seurat. 



The internal median tooth tripartite and very lai'ge, passing 

 over the small external tooth. 



2nd group of Ph. clansa Rud. 



The external and median teeth are of the same height. 



3rd group of Ph. alata Rud. 



The external tooth is very large and triangular ; the internal 

 tooth (tripartite) is small. 



4th group of Ph. abhreviata Rud. 



The external tooth is enormous and triangular ; the internal 

 tooth is very small and difficult to see. 



If Ave adopt this division, we would be obliged to add a 

 5th group of Ph. coluh-i (Rud.), Dies., characterised by the 

 presence of a large and triangular external tooth and the entire 

 absence of the internal median tooth. 



In subdividing any group of animals, our first aim is to bring- 

 together those forms which possess close affinities to each othei-, 

 and not those forms Avhich, when grouped together, render it 

 easier or more convenient to us to determine them. Seraut"s 

 divisions, when submitted to this test, are consequently not 

 tenable, as it would imply that all the polydelplioid foi-ms are 

 closely related to such didelphoid forms as Ph. prceptotialis and 

 Ph. maxillaris. 



Assuming that the line of evolution has proceeded from the 

 didelphic to the polydelphic forms, then, I think, we have to 

 recognise two vvays, both starting from a form with genitalia of 

 the Ph. clcmsa (text-fig. 1 A) type. The one group would evolve 

 from this type thi-ough stages like Ph. prceputialis (text-fig. 1 B), 

 Ph. tumefaciens (text-fig. 1 C) to Ph. titrgida (text-fig. 1 I)), and 



