18 ON SOME INSECT DEFORMITIES. 



splitting is not the same for all Lepidoptera. Most of them split at 

 first the dorsum of the second and third segment of the caterpillar. 

 Pieris cratcegi is stated by Bonnet to split its skin only in the head ; and 

 Reaumur records for Zi/gccna flipendvlce that the caterpillar bites off" 

 pieces of the old skin and puts them aside. Besides those old observa- 

 tions there exists a large number of recent ones. Generally it is true 

 that Coleoptera, Orthoptera, Pseudoneuroptera, Diptera, Hemiptera, at 

 least the Homoptera, and the larger part of Lepidoptera, split first the 

 frontal sutures of the head. 



It is of interest that the well-known Limvlvs Polyphemus splits in the 

 moult the frontal sutures similar to the insects, and goes out forward 

 of the old skin. I find nothing published about the splitting of the 

 skin of the Crustacea. But the Decapods split along the border of 

 the cephalophorax, and are obliged in moulting to take out the parts 

 backwards. As the systematic position of Limulus is still a matter of 

 dispute, I think this fact is of some value. 



The restlessness of the insects before the moult, and the fact that 

 they do not need food, are easily understood. It is known that the 

 tracheas participate largely in the moult. At certain times the inner 

 skin must begin to separate, and it is obvious that through it the respi- 

 ration will be impeded. Perhaps this difficulty has something to do 

 with the acceleration of the blood. Besides the tracheae a large part 

 of the digestive canal changes its skin ; the anterior part to the ven- 

 triculus, and the posterior to the colon. Here also, at a certain time, 

 the inner skin begins to separate, and the natural consequence will be 

 the impossibility of taking any food, or even of ejecting the superfluum 

 contained in the intestines. 



All insects, as I stated before, go forwards out of the old skin in 

 transformation. But I find one case of the contrary quoted by Profes- 

 sor Westwood (Brit. Cyclop. Article Insect, p. 844). He says that Coc- 

 cus comes out backward, the wings rejected above the head. 



A very remarkable fact is that the females of the Ephemerous genus 

 Palingenia do not change the skin of the subimago. Swammerdam 

 says the females for the most part do not change the skin ; but a very 

 large number of them examined by myself possessed the subimago 

 skin, and I never saw one without it. They undergo copulation and 

 lay eggs without having arrived at the state of a perfect insect. 



The instances where insects in the last moult are not able to throw 

 away the skin and carry it with them are in Ephemera not very rare, 

 as the long setae are sometimes fastened in the old skin. But I caught 

 a Libellula flying with its nympha skin fastened to the end of the abdo- 

 men. The specimen, Diplax scotica, is still in my collection. I am 

 indebted to Mr. A. Agassiz for a knowledge of the fact that larvae of 

 Radiates are sometimes found with parts of the foregoing state still 

 attached to the skin. 



