202 [November 



Hence we may conclude 1st, that tessellaris may, witliout very ma- 

 terial injury to its health, be shifted on to Oak from the other trees on 

 which it naturally feeds; for although, of those that were retained on 

 Oak, a much larger percentage spun up than of those that were shifted 

 on to Oak from other trees, yet a considerable percentage of the former, 

 and none whatever of the latter, died in confinement. 2nfJ. That Syc- 

 amore is not a congenial food i'or tessellaris ; for a considerable percent- 

 age of those fed on Sycamore died in confinement, and but a small per- 

 centage spun up. Srd. That Oak is abhorrent to Harrisli as a food- 

 plant. — It may seem strange at the first view, that tessellaris can be 

 compelled to feed upon Sycamore up to the time of its assuming the 

 pupa state, and Harrisii cannot be compelled to feed for any length 

 of time upon Oak ; but when we consider that in a state of nature the 

 former is polyphagous and the latter monophagous, our surprise will 

 cease. It is not that Harrisii does not eat the oak-leaves furnished to 

 it — for the quantity of excrement on the floor of the Breeding-cage at 

 each shifting and cleaning out proved that it must eat them — but that, 

 having eaten them, it either perishes of disease superinduced by the 

 unnatural food, or bores its way out in despair through the millinet of 

 the Cage, or devours its own brethren in default of its natural food- 

 plant. 



It will be observed from the Table that in Nos. 5, 6 and 7 the ave- 

 rage number of days when the larvae were found missing is small, being 

 only a little over four days; whereas in Nos. 3 and 4 it is large, being 

 a little over sixteen and a half days. The reason of this difierence is, 

 that in the former, as soon as the larvae were placed on the leaves, they 

 commenced endeavoring to escape ; whereas in the latter, they mostly 

 staid contentedly on the leaves until they were full-grown, when many 

 escaped from the Breeding-cage, probably in search of a more conve- 

 nient place in which to spin up. 



On the whole — -however disagreeable it may be to systematists to 

 concede, that two perfectly distinct insects may be undistinguishable in 

 the imago state, and consequently that something more is necessary, to- 

 wards the definitive establishment of specific distinctions, than the mere 

 comparison of cabinet specimens of the imago — we must, I think, in 

 view of all the above facts, decide that tessellaris and Harrisii do not 

 belong to the same species. If, indeed, we first lay it down as a law, 

 that all forms that are undistinguishable in the imago are identical, 

 then all such facts as the above will go for nothing. But to do this is 

 merely begging the question and arguing in a vicious circle. We might 



