62 TRANSFORMATIONS OF INSECTS. 



drawn under the posterior margin of the one which immediately 

 precedes it. This occurs in all the segments which form the 

 abdominal region of the future moth, the nine posterior ones of the 

 larva. When the period of changing into the pupa state has 

 arrived, a much greater shortening takes place in the muscles of 

 the fifth and sixth segments, and in some insects this is carried to 

 so great an extent, that the whole body becomes constricted in the 

 fifth segment like an hour-glass, and is thus divided into two dis- 

 tinct regions — the thorax and abdomen. The same change takes 

 place also in the muscles of the first and second segments, by 

 means of which the region of the head is divided from that of 

 the thorax. The fifth segment becomes almost entirely atrophied, 

 and the sixth very much shortened. A part of the fifth segment 

 forms a portion of the posterior surface of the thorax of the 

 perfect insect, while the remainder constitutes the petiole or neck 

 which connects the abdomen with the thorax, the sixth being 

 the first true segment of the abdominal region." 



The engravings of Vanessa nrticcs (page 41) will assist in the 

 comprehension of these changes, as will also the drawing of the 

 larva, pupa, and moth of Sphinx ligiistri. In this last engraving 

 the segments are marked so that the alterations in the three 

 phases may be recognised. 



" Exactly the same changes take place in hymenopterous insects, 

 and in every other species in which we have had opportunities 

 of watching them. It is the opinion of Dr. Ratzeburgh, that the 

 head in hymenopterous insects is composed of two segments of 

 the larva, because just before the change into the nymph or pupa 

 state, a portion of the head is found beneath the integuments of 

 the second segment. The fact is indisputable, but the explanation 

 of it appears to be this : — The true head of the hymenopterous 

 larva consists of but one segment, which is provided with the 

 organs of manducation and sensation, the same as in the Icpi- 

 doptcra ; but the head in this larva ceases to become larger 

 after a certain period, while the other segments of the body 

 continue to grow, and ultimately acquire a diameter more than 

 double that of the head. Now the parts which are to form the 

 head of the future nymph continue also to grow beneath the 

 unyielding cranium, from which, as the change approaches, they 



