60 BRITISH LEPIDOPTERA. 



guishes male Dendrolimus pini larvae from female larvas : (1) By the 

 smaller size. (2) By the lighter, almost smoky-grey colour. (3) By 

 a black- brown band situated beneath the second pair of prolegs. 

 (This band is said to be only obscurely marked in the female). 



Jackson says that the larval ovaries are situated in the 5th abdo- 

 minal somite, and close to the dorsal middle line. Their proximal or 

 attached extremities are approximated, and they diverge from one 

 another posteriorly. The colour gets deeper during the quiescent 

 period preceding pupation. Four opaque white lines, the future ovari- 

 oles, traverse the larval ovaries lengthwise and converge towards 

 their hinder extremities, from which the larval oviducts spring. The 

 latter are very delicate filaments, and difficult to make out. 



Bessels gives the following table of species in which the larval 

 testes and ovaries are dissimilar in colour : 



SPECIES. OVARY. TESTIS. FAT-BODY. 



Porthetria dispar ... yellow . flesh-red . white 



Ccsmotriche potatoria yellow 



Deilephila euphorbiae yellow 



Pier is brassicae ... yellow 



Cossus ligniperda ... white 



yellow 

 reddish 

 violet 

 white 



white 

 yellow 

 white 

 white 



Jackson adds that, in these particulars, the larvffi of Sphinx liyustri 

 and Phalera biicephala agree with Cossus. In Pier is brassicae the fresh 

 fat-body posteriorly to the 6th segment is greenish or olive-yellow, 

 anteriorly to it opaque yellow or green on the dorsal aspect, but on the 

 ventral aspect white. The fat-body of the larva of Vanessa io is yellow, 

 and becomes orange in the pupa (Trans. Linn. Soc. Loml., Zool., 

 vol. v., p. 159). 



With regard to the point of development reached by the sexual 

 organs in the lepidopterous larva, it would appear that they have 

 developed as far as that reached by the adult (imago) Ephemerid (May- 

 flies). In the imagines of the Lepidoptera, the two oviducts unite, and 

 form a single tube down which the egg passes. In the adult Ephemerid, 

 the two oviducts remain separate. In the larva of Vanessa io, the 

 oviducts are separate, as in the Ephemerid imago, but by the time that 

 the butterfly is matured, the oviducts have united to form a quite 

 typical ovipositor. Such a line of evolution, however, suggests that 

 the oviduct of the Lepidoptera passed through a stage similar to that 

 which is to be observed in the Ephemera at the present time, before it 

 reached its present high stage of development. 



CHAPTER VII. 



THE VARIATION OF THE IMAGINES OF THE LEPIDOPTERA. 



THE variation in the colours of insects is so patent to every observer 

 of these interesting creatures, that there is no need for one to attempt 

 to show that variation exists. Superficially examined, we find that 

 the individuals of a given species are very similar to each other, yet the 

 eye of an expert sees minute differences in these individuals, and he 

 knows that just as no two men or women are exactly alike, so no two 



