434 PHYSIOLOGY. 



those of the thorax and abdomen. This dissimilarity is founded upon 

 the more determinate figure divaricating more from the general one 

 which the three segments of the thorax have adopted, a dissimilarity 

 found to exist not only between them and the segments of the abdomen 

 but also between them individually. 



With respect to the second, the histological and morphological sepa- 

 ration, the first we have already superficially touched upon. The 

 tunics of the intestine do not indeed become uniformly more compact 

 and firmer by the metamorphosis, but in general only in those cases in 

 which the perfect insect f takes the same food as the larva, namely, in 

 the Carnivora. In the Lcpidoptera the increased development in- 

 creases the necessity of better and more delicate nutriment, conse- 

 quently the butterfly does not require so compact an intestinal tunic as 

 the caterpillar. The latter has to elaborate and extract the entire sub- 

 stance of the plant, the former merely feeds upon the most delicate 

 juices of flowers, namely, their honey. The thick fleshy proventriculus, 

 armed with horny teeth and plates, most perfectly exhibits the histolo- 

 gical separation. From the thin membranous cardia of the stomach of 

 the larva during the short pupa state this powerful and muscular organ 

 has been produced; from this same thin tunic processes have arisen, 

 and thus its cavity has distended upon all sides. But in conjunction 

 with this the general cavity of the ilium decreases, the muscular fibres 

 contract, and form a compact firmer membrane than that of the stomach 

 of the larva. And lastly, the morphological separation is even more 

 decided ; similar rings transform themselves into the most dissimilar 

 divisions of the body, and in these diAasions large muscles grow from 

 small beginnings, new organs of motion are also associated during the 

 pupa state, and the old ones become lengthened generally as well as 

 in their several joints, and, indeed, what was formerly a single joint 

 becomes divided into from four to five, namely, the tarsus ; or an organ 

 which consisted of three or four joints now exhibits ten, twenty, and 

 sometimes as many as fifty. Eyes even, the most important of all the 

 organs of the senses, originate ; and at a place where previously the 

 situation of the head was indicated, merely by the orifice of the mouth, 

 an entire head is formed with all its requisite organs. 



256. 



The preceding paragraph shows us that the character of the meta- 

 morphosis of insects is found to be now restricted to its progress 



