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POPULAR SCIENCE REVIEW. 
is obvious, since it enables their smooth and polished bodies to 
adhere to the particular weeds on which they are found, whilst 
these are swayed to and fro by the currents of the tide, or by 
the breaking of the waves over the rock pools. Then, again, 
there is a marked difference in the number of ova or young 
produced : whilst the parasitic species are most prolific, furnish- 
ing offspring by hundreds, thousands, or even millions, and the 
ova are minute, in the free Nematoids the ova are relatively 
very large and few in number, being easily countable, and when 
mature in some species they occupy almost the whole width of 
the body. This is a state of things quite in harmony with the 
totally different conditions of life of the respective animals. 
The free Nematoids produce their ova or young at once in that 
environment which they are destined to inhabit, whereas the 
parasitic offspring are subjected to the influence of a multiplicity 
of chances and adverse agencies, before they can meet with the 
conditions suitable for their development : this necessarily entails 
much waste. 
Adopting a name which was first given to these animals by 
MM. Grervais and Van Beneden, the family Anguillulid.e is 
now known to include about 180 species, of which more than 
100 have been found in this country, and I feel confident that 
if a diligent search were made in the British Isles by a few 
zealous observers, the number of species belonging to our fauna 
might be doubled, or even quadrupled, within the course of a 
very few years. This may sound like over-sanguine prognosti- 
cation, but I have an adequate foundation for the belief, based 
upon my own experiences in the search after these animals, and 
the abundance of specific forms met with in a few localities only. 
With regard to the past history of the group I may say that 
Dujardin discovered several new species, and was the first to 
give anything like an accurate description of some of these 
animals. Eberth has, within the last few years, described 
many new species found on the Italian sea-coast. Schneider 
of Berlin has also described many new forms, and our country- 
man Carter has added ten new species to the list, these having 
been discovered by him in Bombay."^ Other workers in 
this field who have contributed single or smaller numbers of 
species are Borellus, Baker, Spallanzani, IS'eedham, Otto Muller, 
Bory, Stein buch, Duges, Ehrenberg and Hemprich, Nordmann, 
Dujardin, Oken, Quatrefages, Orube, Leuckart, Diesing, Max 
Schultze, Leidy, Kiihn, and Cobbold. The first animal of this 
family that was discovered, happened to be the so-called 
* Ann. and Mag. of Nat. Hist. Third Series. July, 1859, In addition 
to the habitats I have mentioned, I may state that Carter has found some 
of these animals- very abundantly in the substance of large fungi. 
