ITS OUTER SKELETON. 41 



familiar fact that in many larvae the antennae are placed further 

 forward than in the adult. The three large joints at the base 

 of Orthopterous antennae have been taken to correspond with 

 those of Crustacean antennules, and it has been inferred that in 

 Insects with incomplete metamorphosis, only antennules or 

 larval antennae are developed.* This reasoning was never very 

 cogent, and it has been impaired by further inquiry. Weismann 

 has shown that in Corethra plumicomis, the adult antenna, 

 though inserted much further back than that of the larva, is 

 developed within it,t and Graber has described a still more 

 striking case of the same thing in a White Butterfly.:}: There 

 is, therefore, no reason to suppose that Insects possess more than 

 one pair of antennae, which is probably preoral, not correspond- 

 ing with either of the Crustacean pairs. 



We have already noticed (p. 26) the superficial points in 

 which the antenna of the male Cockroach differs from that of 

 the female. 



The eyes of some Crustacea are carried upon jointed appen- 

 dages, but this is never the case in Insects, though the eye- 

 bearing surface may project from the head, as in Diopsis and 

 Stylops. Professor Huxley supposes that the head of an Insect 

 may contain six somites, the eyes representing one pair of 

 appendages. The various positions in which the eyes of Arthro- 

 poda may be developed weakens the argument drawn from the 

 stalk-eyed Crustacea. Claus and Fritz M tiller go so far on the 

 other side as to deny the existence of an eye-segment even in 

 Crustacea. 



Mouth-parts of the Cockroach. 



Before entering upon a full description of the mouth-parts of 

 the Cockroach, which present some technical difficulties, the 

 beginner in Insect anatomy will find it useful to get a few 

 points of nomenclature fixed in his memory. Unfortunately, 

 the terms employed by entomologists are at times neither 

 convenient nor philosophical. 



* Zaddach, Entw. des Phryganiden Eies, p. 86 ; Rolleston, Forms of Animal Life, 

 p. 75, &c. 



t Zeits. f. wiss. Zool., Bd. XVI., pi. vii., fig. 33. 



J Insekten, Vol. II., p. 508. 



Anat. Invert. Animals, p. 398. 



