June 8, 1917] 



SCIENCE 



593 



SEGMENTATION IN NEMATODES: 

 OBSERVATIONS BEARING ON THE UNSETTLED QUES- 

 TION OF THE RELATIONSHIP OF NEMATODES 

 TO OTHER BRANCHES OF THE 

 ANIMAL KINGDOM 



I HAVE long been impressed by certain evi- 

 dences of segmentation in nematodes. My 

 first impressions arose from a study of the 

 distribution of the setse on aquatic forms. 

 Tliis distribution was in those days, and is 

 even yet, described as irregular; the setse are 

 eaid to be " scattered " on the body. Charting 

 all the setffi on a given specimen led to the 

 conclusion that they were not scattered 

 (" zerstreut ") ; that, rather on the contrary, 

 they constituted a series of more or less har- 

 monious groups. The cephalic setse, it is well 

 known, have an orderly arrangement. The 

 study of a large number of cases leads me to 

 the conclusion that those setse, some distance 

 behind the cephalic setse, denominated sub- 

 cephalic setse, are also orderly in arrangement, 

 and might, in some instances at least, be re- 

 garded as repetitive of the cephalic setse. 



Later I was able to show that the transverse 

 strise of the cuticle are retrorse on the poste- 

 rior 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 there- 

 abouts, occurs in a very wide range of genera, 

 is independent of age and of sex, and seems a 

 character of fundamental significance. 



Pig. 1. DiAGEAM or the Eevbrsal oi the 

 Stei^ op the Cuticle of a Nematode. 



Eecently I have discovered that the prin- 

 cipal cephalic organs are made up of segments 

 which, while simple in character, bear no small 

 resemblance to corresponding features in 

 arthropods. The nature of these segmented 

 appendages will be more easily understood by 

 consulting the illustrations in Fig. 2. 



The articulations in the cephalic organs of 

 nomas are not easy to discover, owing to the 

 small size of the organs and the transparency 

 of the tissues. Some of these segmented 



organs are under muscular control, and can be 

 extended and inflexed after the manner of the 

 palps of insects. This is true of some of the 

 labial organs, which unfortunately are usually 

 so small as to be difficult to observe. The 

 cephalic setse, however, are larger, being par- 

 ticularly well developed on some marine forms, 

 and in this case observation on living speci- 

 mens affords evidence of the .articulations when 

 they might be overlooked if they were sought 

 by other methods; for if a seta is obstructed 

 it takes on the attitude natural to an organ 

 composed of flexible joints and more or less 

 inflexible segments, as shown in the upper 

 illustration. Fig. 2. Here again, once having 

 established the fact and learned how to make 

 the observations, it proves that the setse of a 

 wide range of genera are jointed, though the 

 number of segments is often reduced to only 

 one or two. 



Fig. 2. Cephalic Seta op a Nematode, show- 

 ing Segmentation. Two Dipferent AttitudbS 

 OF THE Same Seta. 



One recalls that a number of observers have 

 noted the presence of longitudinal series of 

 repetitive organs in the lateral fields of nema- 

 todes, though attention has never been called 

 to the fact that these organs on opposite sides 

 of the body may be symmetrical to each other. 

 Sometimes they are exactly so. 



IvT. A. Cobb 



SOCIETIES AND ACADEMIES 



THE BOTANICAL SOCIETY OF WASHINGTON 

 The 119th regular meeting of the Botanical So- 

 ciety of Washington was held at the New Ebbitt 

 Hotel, on March 14, 1917. Seventy-four mem- 

 bers and sixty-five guests were present. After a 

 dinner President T. H. Kearney introduced the re- 



