ANGUILLULID^. 55 



AngmllulidcB. — Here may be conveniently brought together a 

 vast number of minute thread-worms, whose intimate organization 

 and course of development is not yet well understood, but whose 

 general anatomy is so far known that we need have little hesitation 

 in placing them along with the other nematode families. Some of 

 the obscurer genera may turn out to be annelids, and a more 

 correct classification will thus be ultimately adopted. A con- 

 siderable number of the AnguillulidaB are non-parasitic, at least, 

 so far as animals are concerned ; a few are believed to be so alto- 

 gether. Some of the species are found in moist earth, in sour paste, 

 in vinegar, and in various vegetable matters undergoing acetous 

 fermentation ; while others occur endo-parasitically in earthworms, 

 in aquatic moUusks, in the larv^ of beetles and other insects, in 

 the alimentary canal of batrachians, and also in the digestive 

 system of fishes. Some are oviparous, others viviparous. Nearly 

 all appear to possess a remarkable tenacity of life, and in certain 

 species this phenomenon is truly astonishing. Thus, in Anguillula 

 fluviatilis, the body may become entirely dried by exposure to the 

 sun's rays, but the animal will revive immediately after moistening 

 by a shower of rain. In like manner, many of the species may 

 be frozen without destruction to their hfe ; but, on the other hand, 

 some of the forms will bear neither the extremes of heat nor cold ; 

 in a few instances, it is said that the application of a moderate 

 heat will prove fatal. In the case of Anguillula tritici, where the 

 life-tenacity is most strongly marked, the observations of Trembley, 

 Needham, Bauer, Dujardin, and others, have shown that the 

 animal is capable of revivification after complete desiccation ex- 

 tending over a period of four or even five years. 



Selecting the common vinegar eel (A. aceti) as a type, we have 

 a filiform body about forty times longer than it is broad, and seldom 

 attaining one-twelfth of an inch in length. Some are said to have 

 measured one quarter of an inch from head to tail, but it is most 

 common to find them about half a line, or in the case of the females, 

 from one to two or more milimetres long. The front of the body is 



