452 ARABIAN NEMATODES, 



bring into balsam by means of the diiferentiator. Most of the 

 smaller species stain readily in borax carmine, which is one of the 

 best of stains for this work. Oxytcris vermiculai'is (adults, not 

 the young) and a number of other parasitic species, however, do 

 not stain in borax carmine. Mayer's carmine rarely fails to stain 

 these exceptional species. Overstaining is corrected by adding 

 hydrochloric acid to the proper differentiator fluids. I can recom- 

 mend this method very highly, not only for Anguilhdidce, hut also 

 for numerous other groups of the smaller animals and plants. 



Formula. 



I intend to describe in a series of papers, of which this is one of 

 the first, a large number of hitherto unknown Nematodes. In 

 order to bring the characterizations into small compass, and thus 

 gain space for the fuller discussion of such morphological, physio- 

 logical, and pathological problems as may present themselves, I 

 shall make use of a new formula which expresses briefly and 

 accurately the necessary measurements. 



Inasmuch as this formula will occur once or twice in the descrin- 

 tion of each species, and be made to bear such a large share of the 

 burden of characterization as to become, in a systematic sense, a 

 prime factor in the work, it merits at the outset a full elucidation. 



Since the middle of the present century nematelminthologists 

 have shown an ever-increasing regard to absolute and relative 

 dimensions. Dujardin (1846) gave the length, the ratio between 

 the length and breadth, and occasionally other dimensions, such as 

 the length of the tail and the position of the vulva. No one did 

 more than this until Eberth and Bastian, working simultaneously 

 on the Anguillulidse, saw the necessity for further particularization. 

 These two investigators, the one in Germany, and especially the 

 other in England, laid firm the foundation of the important super- 

 structure afterwards raised by Biitschli, Marion, De Man, Von 

 Linstow and others. The appearance of their works (Eb. 1863, 

 Bast. 1866) marks an era in the history of our knowledge of the 

 group of which they treated. Their texts were accompanied by 



