136 



BRISTLE-TAILS AND SPRING-TAILS. 



157. Head of De- 

 geeria. 



cranium) by a V-shaped suture * (Fig. 157, head of Degeeria ; 



compare also the head of the larva of Forflcula, Fig. 158 ? in 



which the suture is the same), and the insertion of the antenna 



is removed far down the front, near the mouth, 



the clypeus being very short; this piece, so 



large and prominent in the higher insects, is 



not distinctly separated by suture from the 



surrounding parts of the head, thus affording 



one of the best distinctive characters of the 



Poduridas. The eyes are situated on top of 



the head just behind &quot;the antennae, and are 



simple, consisting of a group of from five to 



eight or ten united into a mass in Smynthurus, 



but separated in the Poduridac (see Fig. 17G, e, eye of Anurida). 



The antennas are usually four- 

 jointed, and vary in length in the 

 different genera. 



The mouth-parts are very diffi 

 cult to make out, but by soaking 

 the insect in potash for twenty- 

 four hours, thus rendering the 

 body transparent, they can be 

 satisfactorily observed. They 

 are constructed on the same gen 

 eral type as the mouth-parts of 

 the Neuroptera, Orthoptera and 

 Coleoptera, and except in being 

 degraded, and with certain parts 



obsolete, they do not essentially differ, f On observing the living 



Podura, the mouth seems a simple ring, with a minute labrum 



and groups of hairs and spinules, which the observer, partly by 



*Thc direct homology of these parts of the head (the occiput and the epicra- 

 niuni) with Perla, Forflcula, etc., seems to me the best evidence we could have that 

 the Podura; are not an independent group. In these most fundamental characters 

 they differ widely from the Myriopods. J[ am not aware that this important rela 

 tion has been appreciated by observers. 



fAs we descend to the soft, tube-like, suctorial (?) mouth of Anura, which is said 

 not to have hard mouth-parts, we see the final point of degradation to which the 

 mouth of the Thysanura is carried. I think that this gradual degradation of the 

 mouth-parts in this group indicates that the appendages in these animals are not 

 formed on an independent type, intermediate, so to speak, between the mandibnlate 

 and haustellate types, but are simply a modification (through disuse) of the man- 

 dibulate type as seen in Neuropterous insects. 



158. Larva of Forficula. 



