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yet in the egg; or in water, perhaps shallow from the first, 
which has dried up, causing the gills to be cast off prematurely, 
and the tadpole form to cease at once. 
These last cases are striking instances of nature adapting itself 
to external conditions, and altering its course according as these 
alter. ‘ 
The Surinam toad may be just alluded to as a singular case in 
which the young are not only always born perfecily formed, but 
they are reared in small cells in the mother’s back, in which the 
eggs are carefully deposited by the male, as soon as laid by the 
female. There they remain till they are hatched.* 
We have yet to consider the case of full development in one sex 
only. This takes place in certain species of moth, the females of 
which are apterous and sluggish, nearly colourless—though the 
colours may be dark and well defined in the other sex, and more 
like great fat maggots than real moths to which, in outward 
appearance, they show scarce any affinity. 
This form of arrested development is well seen in the females 
of the moths called Vapourers by English collectors,+ (Orgyia). 
In some of the foreign species of this genus the females are not 
only apterous, with very short legs, but they actually never leave 
the coccoon at all, “having intercourse with the male through 
a hole at one end of it.” 
I now proceed to draw your attention to several changes of 
form occurring in the class of fish. The first relates to the 
remarkable difference between the young and the adult in the 
case of what we all well know as flat fish. We are familiar with 
* See a representation of this toad in Shaw’s Naturalists’ Miscellany, 
vol. i., pl. 17. 
+ Orgyia antiqua, Steph. Brit. Ent. Haust., vol. ii., p. 61. Coloured 
figures of both sexes of this insect, under the name of Phalzna antiqua, 
may be seen in Donovan's British Insects, vol. i., pl. 16. 
t Lntomol. Trans., 3rd series, vol. i., Proceed. p. 70. 
a — eee 
