420 HETEROCHROSTS 
elsewhere as 4. fluvicollis,—one form of which, 4. gouldi, inhabits 
Australia. 
The true Bitterns, forming the genus Botaurus, have been 
already noticed (pp. 40-42); and of the Night-Herons Schlegel 
recognized six species, all to be reasonably placed in the genus 
Nycticorax, characterized by a shorter beak and a few other 
peculiarities, among which the large eyes deserve mention. ‘The 
first is N. griseus, a bird widely spread over the Old World, and 
not unfrequently visiting England, where it would undoubtedly 
breed if permitted. The same author united with it the common 
Night-Heron of America; but this, though very closely allied, is 
generally deemed distinct, and is the NV. nexvius or N. gardeni of 
most writers. A clearly different. American species, with a more 
southern habitat, is the NV. violaceus or N. cayennensis, while others 
are found in South America, Australia, some of the Asiatic Islands, 
and in West Africa. The Galapagos have a peculiar species, J. 
pauper, and another, brevipennate and no doubt peculiar, NV. mega- 
cephalus, existed in Rodriguez at the time of its being first colonized, 
but is now extinct. To this section undoubtedly belongs the Boat- 
BILL (p. 45), though it deserves generic distinction as Cancroma.! 
Bones of the common Heron and Bittern are not uncommon in 
the peat of the East-Anglian fens. Remains from Sansan and 
Langy in France have been referred by M. Alphonse Milne-Edwards 
to Herons under the names of Ardea perpleaa and A. formosa; a 
tibia from the Miocene of Steinheim by Dr. Fraas to an A. similis, 
while Sir R. Owen recognized a portion of a sternum from the 
London Clay (see above, pp. 281, 282) as approaching this Family. 
It remains to say that the Herons form part of Prof. Huxley’s 
section Pelargomorphex, belonging to his larger group Desmognatha, 
and to draw attention to the singular development of the patches 
of “ powder-down ” which in the Family Ardeide attain a magnitude 
hardly to be found elsewhere. Their use is utterly unknown. 
HETEROCHROSIS, the collective term signifying the occur- 
rence of abnormal coloration which may be due to one or other of 
various causes, such as 
1. The partial or total absence of pigment producing a paler 
hue or even a complete ALBINO. 
2. The overproduction of pigment resulting in a more intense 
tint or the introduction of a new colour. ‘ 
3. The absence of or change in the surface overlying the pigment. 
There seems to be a certain correlation of colours in most cases 
of Heterochrosis: for instance, feathers with a yellow pigment 
have a tendency toward orange and red; green feathers exhibit 
1 The Sun-BiTTERN (Lurypyga), by some systematists considered to belong to 
the Ardeidx, certainly forms a Family by itself. 
