hearing on the origin of Insects. 149 



the important fact that these appendages are jointed and 

 articnlated to the head just as in the Chilognathous 

 myriopods. The joints, however, are not movable, but, 

 on the contrary, quite stiff", the process of modification 

 suggested below having apparently already commenced. 

 The posterior ball-shaped condyle of mandibulated insects, 

 clearly foreshadowed in the myriopod, is here fully formed 

 and provided with a distinct neck ; it is a process of the 

 minute basal joint (1, fig. 1), which is indicated by a dis- 

 tinct inflection of the integument ; the second joint (2 + 3 ) 

 answers to the second and third in the myriopod ; and the 

 third and apical free one (4) has a well-developed molar 

 tubercle at the base of its long, knife-shaped incisive pro- 

 cess, which is obscurely toothed, or, rather, creuulated, on 

 the inner extremity ; it is marked off from the preceding 

 joint by a conspicuous constriction as well as by a circum- 

 ferential inflection of the integument. The two basal joints 

 form almost the whole of the side of the head, as in the 

 Cliilognatlia, that is to say, roughly speaking, the part 

 corresponding to the so-called 'gena' in Blatta; they ter- 

 minate where the apical joint begins, at a point approxi- 

 mately answering to the position of the ' ginglymus ' in 

 Blatta. The great flexor muscles are inserted into the 

 inner face of the outer wall, and pass thence through a 

 cleft in the opposite wall of the second joint to be attached 

 to a median chitinous plate ; so that, just as in Chilog- 

 nathous myriopods, the two mandibles come away attached 

 together when it is attempted to dissect out either one of 

 them. 



In the ripe embryos of ^Blatta'' {Panesthio^ Javanica 

 previously alluded to, two deep folds* are to be seen in 

 the integument of the 'back' of the mandible, between 

 the base of the apical crushing and cutting part of the 

 appendage and the condyle ; they pass across both sides of 



* Folds not of the larval skin previonsly referred to, but of the integu- 

 ment of the enclosed appendage, in the interior of which the definitive 

 non-jointed mandible is plainly visible by transmitted light, and is almost 

 ready for use. In all the ametabolous Insects, the mandibles and the 

 claws of the feet are never for a moment useless to their possessors, but 

 are continuously in use from birth to death, the portion of the thin cxuviuni 

 that covers the parts being worn away by use, and the new jaws and claws 

 exposed, before tlic moult takes ])lace. In both the species of Fvrlpatus 

 dissected by me, not one only but two jjairs of these reserve jaws arc 

 present, that is to say, there ai'e two claws in different stages of develop- 

 ment in the interior of each of the functional ones. This phenomenon 

 appears to be universal in Arthroiwda, ThorcU ('Monograph of Argu- 

 lUl(c') having observed it in Arrfvln.t, and Ilollis (' Journ. Anat. and 

 I'hys.'), in some of our indigenous terrestrial Isopoda. 



