BY N. A. COBB. 179 



species. The connection seldom reaches that state in which 

 it became early known in A s c a r i s 1 u m b r i c o i d e s, where 

 the vessels are actually embedded in the suVjstance of the fields. 

 More often the vessels are simply attached to the fields by con- 

 nective tissue, in which case all cross-sections emphasize the fact 

 that the connection is mechanically wrought and of no deep 

 significance. This is strikingly the case for instance in sections 

 of two species of A s c a r i s whose structure is well known to me, 

 Ascaris Kukenthalii from whale and Ascaris bulbosa 

 from seal of the Arctic Ocean.* 



Granted that the connection between the lateral fields and the 

 lateral vessels, intimate as it sometimes seems, is as it were 

 accidental, we have, in order to prove the homology of the vessels 

 with the one-celled ventral organ of the free-living Nematodes, only 

 to reconcile the duplex nature of the vessels with the more simple 

 nature of the unicellular gland. This can be very conclusively done. 

 In the first place it is to be observed that it remains to be seen 

 whether a duplex form of this organ does not occur ^among free- 

 livinsc forms. I think there is reason to believe that it exists 

 there and is perhaps even not uncommon. In the second place it 

 is to be observed that in the large parasitic worms 'the organ is 

 often, to say the least, single. In the third place the large size 

 and consequent different shape of the organ in the parasitic Nema- 

 todes simply accords with their larger size. Should a typical free- 

 living Nematode three to four inches long ever be discovered I 

 .should be surprised to learn that the ventral gland was a unicellular 

 organ of the form familiar in O n c h o 1 a i m u s and other free- 

 living genera. In the fourth place, and here we return to our 

 O xy u r i s larv», it seems that the development of the organ in 

 the parasitic species is such as to set the matter quite at rest, if 

 we trust ontogenetic evidence. The full grown excretory organ in 

 the genus O x y u r i s is well known to consist of four vessels 

 oi-iginating in a ventral ampulla and extending two forwards and 



* Cobb, "Beitriige z. Anatomic unci Ontogenie d. Nematoden," Jenaische 

 Zeitschrift, XXIII. Bd. N.F. XVI.; also Arcliiv fur Naturgeschichte, I. B., 

 2 Heft, 1889. 



