92 MR. H. CHARLTON BASTIAN’S MONOGRAPH 
readily recognizable. The exact structure of the pharynx and œsophagus, the nature of 
the integumental markings or striæ, and the position and character of the duct of the 
ventral gland seem to me the other characters which, from their constancy, should le 
most relied upon in the construction of genera. The necessity of absolute Accuracy con. 
cerning these details cannot be too strongly enforced, in view of the crude generalities 
which have been offered by some preceding observers as specific descriptions, many of 
which are absolutely useless as a means of identification, and serve only to swell the 
number of synonyms and uselessly perplex subsequent workers in the same field of 
research’, 
Family ANGUILLULIDE, Gervais & Van Beneden. 
Free Nematoids.— Body cylindrical, tapering more or less at either extremity. Ji. 
tegument transparent, striated or plain; naked, or provided with papillæ or setæ; tra- 
versed by capillary pores; shed and renewed at intervals. Caudal sucker mostly pre- 
sent. Glandular system well developed; often single excretory organ in anterior part 
of ventral region. Lateral lines existing as cellular canals communicating with the 
exterior, with or without a central channel; in others replaced by distinct vessels. 
Median lines indistinct. Nervous system, none. Ocelli, when present, aggregations of 
reddish pigment on anterior part of cesophagus, with or without transparent lens-like 
bodies. Generative organs—female, composed of double symmetrical uteri and short 
reflexed ovarian tubes, with vagina near centre of body ; vagina occasionally more poste- 
rior, with posterior uterine segment and ovary undeveloped ; ova few, large: male, con- 
sisting of an almost simple seminal tube, and two equal horny spicules, either alone or 
with one or more accessory pieces. 
' The best method of detectin 
g and capturing these animals I have found to consist in separating with ordinary 
microscopical teasing-needles the 
Specimens of algæ or coralline into small fragments, on the surface of a square piece 
of glass’ covered with a thin stratum of fluid, the glass being laid either upon a black surface or, better still, upon a 
small mirror, when the larger species may be recognized with the naked eye, and the smaller with an ordinary watch- 
— s lens. They are best captured by taking them up upon the pointed extremity of a feather. I have employed 
an ordinary quill pen, with its upper extremity cut off obliquely. In the case of marine or freshwater mud, it should 
be spread out with a little water into a very thin stratum, when, in a minute or so, various spots of disturbance wil 
indicate the position of these or other minute animals. 
I am indebted to the kindness of my friend Howard Fox, Esq., of Falmouth, for being able to pursue in this inland 
ger (Broadmoor, Wokingham) researches concerning the marine Nematoids commenced at Falmouth, since he 
abundantly supplied me at various times with mud, sand, and alge from the estuaries and tide-pools of that place 
