NATURAL HISTORY MISCELLANY. 433 
and action of each separate individual organism, This apparently 
is the keynote of his book. This was the view advocated by the 
speaker, some four years previous in the Memoirs of the Society, 
in a paper written to establish the fact that all characteristics had 
arisen suddenly among the ammonites and nautili of past geolog- 
ical epochs. This paper was a short, preliminary statement of 
facts observed, and it did not excite his surprise that Mivart had 
overlooked it. He could not however help wondering at the ab- 
solute silence preserved with relation to the essay of Professor 
Cope of Philadelphia. This had been issued at about the same 
time and independently, but advocated nearly the same views as 
regarded the sudden production of characteristics among the Rep- 
tiles, and must have been well known to Professor Huxley, with 
whom Mivart seems to have taken council. This omission is by 
no means creditable to the author of a work written to refute such 
books as Darwin is in the habit of producing, and contrasts unfay- 
orably with that writer’s evident acquaintance with the essay al- 
luded to above. This is shown most by the manner in which he 
is obliged to rest the proof of his assertion, that species arise sud- 
denly, upon a number of isolated facts ; whereas either Professor 
Cope’s paper, or the speaker’s, especially the former, would have 
furnished him with a number of reliable and serially connected 
illustrations of the quick evolution of species. 
Parasites. — Prof. Van Beneden, as we have before noticed, 
has distinguished true parasites, which live on their host, from 
commensals, those which. live merely with their host, the thieving 
impostor from the respectable lodger. In an admirable work on 
the “ Fishes of the coasts of Belgium, their Commensals and Par- 
asites ” published by the Academy of Sciences of Brussels, he now 
further classifies parasitic organisms. The commensals are either 
1, Oikosites, fixed; or 2, Coinosites, free. The Oikosites fish for 
their own living, and merely ask a free passage from their hosts. 
They are either fixed in perpetuity, as Coronula, Cochliolepis, 
Modiolaria, Mnestra, and Loxosoma, temporarily as the Remora 
nilocra, Praniza, or only in the young state, e. g., Caligus and 
Anodon. The Coinosites, on the other hand, never give up their 
liberty ; they.occasionally leave their host, and between Coinosite 
and host there is often an exchange of good offices, one furnishing 
a solid house or a strong claw, the other a sharp eye, and they 
