A Nematode Formula. 



Br N. A. COBB, 



I PROPOSE in the near future to describe in a series of papers a large number 

 of bitberto unknown Nematodes. As m-^ny of tbese papers as appear in 

 tbe reports of tbis department will treat of tbose Nematodes wbich live in or 

 upon plants, often tbereby causing diseased conditions wbose nature it is 

 bigbly importaut to understand. In order to bring tbe cbaracterizations 

 into small compass, and tbus gain space for tbe fuller discussion o£ such 

 morphological, physiological, and pathological problems as may present 

 themselves, I shall make use of a new formula which expresses briefly and 

 accurately tbe necessary measurements. 



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

 sionally 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 Anguillulidae, saw the necessity for further particu- 

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

 other in England, laid firm the foundation of tbe important superstructure 

 afterward raised by Biitscbli, 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 accurate and well executed figures of both extremities 

 of each w^orm described. The dimensions given, based sometimes it is true 

 on too few or otherwise too imperfect measurements, related to the length, 

 breadth, position of the vulva, depth of the buccal cavity, and the fraction of 

 the entire length occupied by the tail and oesophagus respectively. To these 

 Bastian added the dimensions of tbe spicula and striae. The English author, 

 making the inch his unit of length, contented himself with giving a categorical 

 list of the measurements made. Thus, taking a species at random, Enopliis 

 ficjmentosus was entered as \ x roo- ; teeth , -\- ; oesophagus, about \ {i.e., 

 of the total length) ; tail, xe-o- This is manifestly not very convenient for 

 the reader. The German author, making the millimeter his unit of length, 

 followed the same plan as his English contemporary but gave fewer 

 measurements, trusting no doubt that the exquisite figures accompanying his 

 text would supply all necessary information concerning details. Biitscbli, 

 the renowned Heidelberg naturalist, followed (1873-4) the plan adopted by 

 Bastian and Eberth, but brought to his aid a greater amount of j)ictorial art. 

 His figures are full length portraits, accompanied by figures on a larger scale, 

 the latter illustrating the details of the head, tail, &c. Marion (1S73) 

 furnished no new ideas to the nomenclaturist. De Man, hoAvever, 

 has introduced decided improvements in nomenclature. Eealizing the 

 116 49—90 (J) 



