PERIODICAL BIRDS TO BECOME TORPID. 105 
In advocating this view of the subject, I am aware 
that I stand opposed to the high authority of Cuvier, 
who, in treating upon the Sand-Martin (Hirundo 
riparia) in the first edition of the ‘Régne Animal,’ 
tome 1. p. 374, asserts, with reference to its supposed 
torpor, that “il parait constant quelle s’engourdit 
pendant l’hiver, et méme qu’elle passe cet état au 
fond de l’eau des marais ;”” and the same opinion is 
reiterated by Humboldt in one of his published 
works ; but as I have not an opportunity of referring 
to them at present, I cannot state in which. Both 
these celebrated authors, however, have omitted to 
communicate the particulars which led them to this 
conclusion ; and the bare assertion even of persons the 
most distinguished in the annals of science cannot be 
received as equivalent to direct evidence. 
It has been stated that the Cuckoo, Swallow, 
House-Martin, and some other species of Periodical 
Summer Birds moult in the interval which elapses 
between the times of their disappearance and reap- 
pearance in this country (see p. 15 e¢ seg.). How 
utterly irreconcilable this plain fact is with the 
hypothesis of their passing that interval in a state of 
torpidity needs scarcely to be insisted upon ; indeed 
it is absolutely inconceivable that birds in a lethargy 
so profound as that in which the animal functions 
seem to be suspended should undergo a change of 
plumage, when Mrs. Warner’s Cuckoo, enjoying all 
