NOTES ON NEMAS* 



(1) Segmentation of Their Organs, Illustrated by three new free-living marine 



genera. (2) Intravitam Color Reactions, (3) the Nema population of Beach 



Sand, (4) Locational Terms for the Cytology of Descent, and 



(5) Functions of the Amphids. 



By N. A. COBB 

 CONTRIBUTIONS TO A SCIENCE OP NEMATOLOGY V 



1 

 SEGMENTATION IN NEMATODES 



OBSERVATIONS BEARING ON THE UNSETTLED QUESTION OF THE 



RELATIONSHIP OF NEMATODES TO OTHER BRANCHES OF 



THE ANIMAL KINGDOM 



I have long been impressed by certain evidences of segmentation 

 in nematodes. My first impressions arose from a study of the dis- 

 tribution of the setae on aquatic forms. This distribution was in 

 those days, and is even yet, described as irregular; the setae are said to 

 be "scattered" on the body. Charting all the setae on a given speci- 

 men led to the conclusion that they were not scattered (" zerstreut") ; 

 that, rather on the contrary, they constituted a series of more or less 

 harmonious groups. The cephalic setae, it is well known, have an 

 orderly arrangement. The study of a large number of cases leads me 

 to the conclusion that those setae, some distance behind the cephalic 

 setae, denominated subcephalic setae, are also orderly in arrangement, 

 and might, in some instances at least, be regarded as repetitive of the 

 cephalic setae. 



Later I was able to show that the transverse striae of the cuticle 

 are retrorse on the posterior half of the body, and the reverse on the 

 front half. (See Fig. 1.) 

 This reversal in the cuticle 

 at the middle of the body, 



Or thereabouts, OCCUrS in Fig. 1. Diagram of the reversal of the striae of the cuticle 

 ., .. of a nematode. The reversal is shown just above the letter F. 



a very wide range of gen- 

 era, is independent of age and of sex, and seems a character of funda- 

 mental significance. 



Waverly Press, Baltimore, May 8, 1917. 



117 



