ANIMALS OF THE ORDER ARANEIDEA. 37 
source known whence they could be derived; and it has been ascertained that if they are 
applied to litmus paper, which has or has not been reddened by acetous acid, they always 
produce upon it effects precisely similar to those caused by the gastric fluid, or rather by 
the fluid contents of the stomach, when subjected to such tests. I may remark that the 
yellow colour of turmeric paper is rendered brown by the application of the fluids from 
the mouth and stomach, and that it is restored again by the agency of the fluid secreted 
by the poison-glands, changes which afford another proof, in addition to those already 
advanced, of the respective alkaline and acid properties of these animal products. 
The instruments employed by the Araneidea to seize and destroy their prey are im- 
properly denominated mandibles; I say improperly, because they actually do not consti- 
tute any part of the oral apparatus, as Mr. W. 8. MacLeay has plainly asserted * ; indeed, 
many eminent zootomists, judging from their position and from the origin of the nerves 
distributed to them, entertain the highly probable opinion that they are the analogues of 
the antennæ of hexapod insects, and in accordance with this view of the subject M. La- 
treille termed them chelicera; but so widely do they differ from antennz in structure and 
function, that the propriety of bestowing upon them a distinct appellation which does not 
imply anything hypothetical will scarcely be questioned: I propose, therefore, to name 
them falces. | 
Much of the misapprehension that exists among arachnologists relative to the falces 
has been occasioned, in all probability, either by the prevailing belief that spiders are 
destitute of a labrum, or by mistaken notions as to its precise situation. That they pos- 
sess the organ in a low state of development is undeniable, as I have distinctly observed 
it in species belonging to the genera Lycosa, Dolomedes, Salticus, Thomisus, Olios, Dras- 
sus, Clubiona, Ciniflo, Agelena, Tegenaria, Celotes, Theridion, Linyphia, Epéira, Dysdera 
and Segestria t. It is attached by its base to the superior surface of the palate, but the 
extremity, which is free and usually round or somewhat pointed, can be slightly elevated, 
depressed, extended, retracted and moved laterally at will. To apply the term mandibles 
to organs originating above the labrum, and therefore not situated within the mouth, 
must evidently be erroneous; and I venture to anticipate, upon anatomical considera- 
tions, that future investigations will lead to the conclusion that the mandibles of the 
Araneidea are confluent with the palate. 
* Annals and Magazine of Natural History, vol. ii. p. 2, note *. 
+ Professor Owen has detected a rudimental labrum in spiders of the genus Mygale. See his ‘ Lectures on Com- 
parative Anatomy,’ Lecture XIX. Arachnida, p. 257. 
