NATURAL HISTORY MISCELLANY. 435 
The stomachs and appendages of fishes swarm with parasites, and 
those which have the largest clientèle are by no means the least 
healthy or thinnest. Often one fish, having swallowed another, is 
swallowed by a third, and thus Xenosites find themselves set free 
in the wrong fish’s stomach, for the stomach acts like a filter, 
straining out and retaining the parasites, while the flesh is di- 
gested. Such erring Xenosites merely wait and may often pass 
through several “hotels” before they reach their destination. 
2nd, Nostosites—those who have reached their destination, and 
now can abandon themselves to generation. Whilst the Xenosite 
was obliged to put up often with an uncomfortable cramped lodg- 
ing, biding his time, the Nostosite occupies the most eligible organs 
for parasitism — in fact, the most vast and commodious chambers 
of the hotel. The 3rd division are the Pilgrims, who have lost 
their way hopelessly, and are in worse plight than even in Giant 
Despair’s castle. Such are the agamic worms which are found 
often in the Plagiostomous fishes, and who ought to have got into 
some Teleostean fish, there to fructify—a happy fate forever lost 
to them when by unlucky chance the host in whom they trusted 
was swallowed by a remorseless shark. They never quit this re- 
treat. 
Prof. Van Beneden gives directions for searching an animal 
for its parasites, and justly claims a high interest for the study of 
« the fauna of individual species, and urges such neat and sharply- 
limited zoological inquiries on those who do not feel prepared to 
study the fauna of a geographical region—to the philosophy of 
which, indeed, the study of parasite-faunz may furnish important 
suggestions. Ninety-three species of fish, with their parasites 
and commensals, are cited in this work from the author’s own o! 
servation. Eight plates illustrate it.— E. R. L., in Nature. 
Tue THEORY or NATURAL Serectrion.—In ‘‘ Nature” for Noy. 10, 
Mr. A. W. Bennett discusses the theory of natural selection, which 
he holds to be inadequate to account for the origin of species. 
Taking as his starting point the two principles laid down by Mr. 
Darwin himself, that natural selection always operates through the 
perpetuation of exceedingly small changes, and that every change 
thus perpetuated by natural selection must be directly beneficial 
to the individual, he applies these principles to the phenomena of 
Mimicry, as illustrated in Mr, Wallace’s ‘‘ Contributions to the The- 
AMER. NATURALIST. VOL. V. 28 
