PROF. AGASSIZ S 



in the larva state, with those of perfect insects. I 

 would, however, except from this criticism some 

 few modern authors, who have followed the glori- 

 ous tracks of the great Entomologists of the past 

 century. Eminent among such exceptional works 

 containing more than descriptive details, stands 

 the remarkable report of Dr. Harris upon the In- 

 sects of Massachusetts injurious to Vegetation, in 

 which the author has given most valuable inform- 

 ation upon the metamorphoses of insects living in 

 this State. Also, Professor Audouir has given 

 many beautifully illustrated facts about the insects 

 injurious to grape vines. Ratzenburg has made 

 similar investigations on insects injurious to the 

 forest trees in Germany. To these works we shall 

 have constantly to refer when studying the meta- 

 morphoses of articulated animals. 



The larvae differ from each other, not only in 

 form but also in structure, and in the successive 

 changes which they undergo. There are larvae 

 which arise from the egg almost under the same 

 form as the perfect insect, and in their metamor- 

 phoses undergo only slight changes of form ; per- 

 haps changing the length of their legs, or modify- 

 ing the apparent number of rings which they had 

 when coming out of the egg. There are others 

 which are born widely different from the perfect 

 insect, which will remain in that form for a certain 

 time, and then change into an Animal entirely dif- 

 ferent in its outline to remain in that condition 

 again for a longer or a shorter period, and then to 

 undergo the last transformation. Insects which 

 undergo such complete changes in form, are called 

 insects with perfect metamorphoses. Those into 

 which changes are introduced gradually, and in 

 which the differences in various periods of life are 

 not so great, are called insects with imperfect met- 

 amorphoses, or half metamorphoses. We have 

 insects in which the young are born under nearly 

 the same form as the perfect insect. I would men- 

 tion the Grasshoppers, for instance, in which the 

 young have the same forms except the wings, 

 which are wanting. The greatest differences are 

 noticed among Butterflies (Plate II, fig, C), where 



[PLATE II CATERPILLAR PUPA & BUTTERFLY.] 

 A 



the Caterpillar is first seen (Fig. A), next the Pupa 

 (Fig. B),and lastly the perfect animal (Fig. C); also 

 in the Beetles (Plate XI, Fig. D). where the form 



represented by figure E, is first seen; next 

 the Pupa (Fig. F), and then the perfect condition 

 (fig. D). Fig. A. represents another Beetle in 

 which the larva (Fig. B) is similar to the Caterpil- 

 lars. In most insects, the larvae, when colorless, are 

 called Maggots, or Worms. In the Ephemera (Plate 

 X, fig. L), we have the same form of the body as 

 is seen in the perfect insect ; but on the sides of 

 the larva there are aquatic respiratory organs, gill?, 

 (Fig, L,) which do no longer exist in the perfect 

 insect (Fig. J). Such cases indicate the extensive 

 differences of structure which may exist among 

 larvae of the same class. 

 [PLATE XI BEETLES WITH THEIR LARVJE AND 



Some (Plate X; nave aquatic Dreaming organs, 

 and others aerial ones a difference which in oth- 

 er departments of the animal kingdom is consider- 

 ed sufficient to divide some of them into different 

 classes. Fishes and Reptiles are not left in the 

 same classes, because the respiration of the one 

 takes place by gills, and in the others, by lungs. 

 You will notice in this figure, (Plate X, fig, L) and 

 in Plate XI, fig A, considerable differences : In the 

 one there are gills, and in the other lung-like or- 

 gans for the same function. 



In others we see still different combinations. In 

 the Phryganea, for instance, (Plate X, fig. H) there 

 are legs only upon the anterior rings, and there aro 

 stiff hairs upon the other rings; whilst in the 

 Caterpillar (Plate II, fig. A) there are legs upon 

 the anterior part of the body; others on the mid- 

 dle joints ; and still others, behind. The larva of the 

 Horse-fly (Plate IX, fig F) has no legs at all, only 

 stiff hairs. In the Mosquito (Plate IX, fig. C) the 

 larva is aquatic, provided with gilis. The pupa 

 (Fig. B) assumes another form, but remains aquat- 

 ic, and finally, the animal appears with legs in a 

 very different form (Fig. A) and with a pair of long 

 wings and various appendages in addition. 



Now, it is important I insist upon this point 

 not only to trace the changes which the larvse un- 



