ROOT-KNOT EELWORM. 



129 



Biology at the Agricultural Experiment Station, Auburn, Alabama.* This 

 work contains the most fully recorded and carefully detailed microscojnc 

 observations of the Heterodera radicicola with which I am acquainted, 

 accompanied by a series of plates giving highly magnified representations of 

 structure. — Ed. 



The male is eel-shaped, slender, and exceedingly minute, being 

 only about one twenty-fifth of an inch, or sometimes a little more, in 

 length, and only seventeen thousandths of an inch in diameter at 

 the middle ; slightly less at the end of the tail ; and in the anterior 

 half the wormlet tapers from the middle to about half the central 

 diameter at the head end. At this extremity is the ccsophagus, or 

 gullet, which is furnished at the foremost end with a minute needle- 

 like point, capable of being thrust out and withdrawn, and technically 



Tylenchus devastateix. 



stem Eelworms, anterior portion of female showing mouth spear ; and embryo 

 in egg ; all greatly magnified : anterior portion magnified 440 times. From figures 

 by Dr. J. Eitzema Bos. 



known as the " exsertile spear." This spear, which rests on a trilobed 

 base, is so very similar to that of the Tylenchus devastatrix, the " Stem 

 Eelworm," which causes Tulip-root in Oat plants, and which has 

 often been referred to in these Reports, that the accompanying figure 

 of this Tylenchus will give a very good general idea of the form of the 

 males and of the young larva of the "Root-knot" Eelworm, the H. 

 radicicola, and also of the position of the spear at the head end. 



• ' A Preliminary Eeport upon the Life-history and Metamorphoses of a Eoot- 

 gall Nematode, Heterodera radicicola (Greef.), Mull., and the Injuries caused by it 

 upon the roots of various plants,' by Geo. P. Atkinson.— Science Contributions from 

 the Agricultural Experiment Station, Alabama, U. S. A., Dec, 1889. 



K 



