LECTURES ON EMBRYOLOGY. 



dergo in their metamorphoses, but also to investi- 

 gate the changes in their structure, which are 

 brought about during their metamorphoses ; and 

 happily we have upon these points most admira- 

 ble investigations by Dr. Herold, though upon 

 only one species, the white Butterfly which feeds 

 apon the cabbage. It is remarkable, however, 

 how few investigations have been made upon these 

 animals at large, when we take all points of view 

 into consideration ; and we find ourselves reduced, 

 for illustration to one single well studied exam- 

 ple. Prof. Kerold in his admirable work begins, 

 unfortunately the investigation only with the full 

 grown Caterpillar, which he goes on comparing 

 with the pupa, and then with the perfect insect. 



Now with reference to these differences between 

 the larvae before I allude to peculiar differences 

 of structure let me make another general remark. 

 There are groups of insects in which considerable 

 differences occur among the larvae even in their 

 structure, wben the perfect insects constitute nat- 

 ural families, and are identical in structure. Again, 

 there are others, the Butterflies for instance, in 

 which thelarvas agree as perfectly as the full grown 

 insects, having alia distinct head (Plate II, fig. A), 

 with powerful jaws, and a slight indication of eyes. 

 Then, we find upon the three anterior rings there 

 are three pairs of legs provided with horny claws, 

 next two rings without legs at all, then, rings with 

 feet of an entire different structure, resembling 

 suckers, then two rings without legs, and a pair of 

 legs upon the last ring. And this arrangement of 

 parts is uniform through all Butterflies. It occurs 

 in the Diurnal as well as in the Sphinx and Noc- 

 turnal Moth. The larva of Butterfly is never an 

 aquatic animal, but is always an air-breathing crea- 

 ture,but there are many aerial insects whose larvae 

 are entirely aquatic. 



Another difference is, that these insects in their 

 lower condition have powerful jaws, by which they 

 chew their food, moving their jaws from right to 

 left and from left to right, on the two sides ; while 

 the perfect animal is very different in having no 

 longer jaws to chew the food, but suckers to take 

 food from the nectar of flowers. And the change 

 in the mode of living is so great, that the Caterpil- 

 ler will consume ten times his own weight of food 

 in a given time, while the perfect animal will not 

 consume more than one tenth of his weight during 

 all the remainder of his life, as a perfect insect 



This fact has great importance in connection 

 with one question about which Naturalists have 

 had much discussion, viz: whether the insects 

 which chew their food should be considered as 

 higher than those which suck their food by suck- 

 ers. The Insects provided with powerful jaws 

 the Beetles, the Wasps, the Bumblebees, Dragon- 

 fliesall these insects, which have powerful jaws, 

 are generally considered higher in their structure, 

 because so many of them are carnivorous, and 

 ' stand in our systems as at the head of insects ; 

 whilst the sucking insects are placed in a lower 



range. That the former are placed higher, arises 

 from no other reason, I think, than the fact that 

 there are so many of them which live upon ani- 

 mal food, or which are properly carnivorous : and 

 as we are accustomed from our intimate acquaint- 

 ance with mammifera to consider Carnivora higher 

 than Herbivora, we are naturally misled to con- 

 sider all carnivorous animals, for th j simple reas- 

 on, that they are carnivorous, as higher than the 

 herbivorous ones. But such impressions can have 

 no value in the estimation of the characters of an- 

 imals of another department. The larvae of many 

 sucking insects have equally powerful jaws as the 

 carnivorous, which are made into another appara- 

 tus of an entirely different structure, introduced in 

 the last transformation of the insect. 



(PLATE V ARTICULATA TRILOBITE.] 



My impression is, therefore, that oc this account 

 we should rather incline for an inverse view of the 

 subject, and an inverse arrangement of the insects, 

 and consider the sucking insects as higher than 

 the chewing Insects. And I would place the But- 

 terflies highest, for the reason that they undergo 

 such extensive metamorphoses passing through 

 so many changes in which the structure grows 

 successively more perfect. That they should be 

 placed highest amongst the sucking insects will be 

 obvious, when we consider that they are aerial 

 worms from the beginning while other insects, 

 with the sucking apparatus, as Flies and Mosqui- 

 toes, constitute a family in which there are many 

 aquatic worms, and we know from other depart- 

 ments, that aquatic animals provided with gill- 

 like apparatus are universally lower in structure 

 than those which breathe air. But such an uni- 

 formity in larvee as we have among Caterpillars 

 is not noticed in other insects. You can of 

 course compare the larva of Dermestes (Plate XI., 

 fig B ) with a Caterpillar, (Plate II., rtir. A.) But, 

 of the external appearances, the appendages of the 

 skin agree ; the arrangement of the feet will be 

 found different. 



The aquatic insects have their larvae still more 

 different, being provided with gills, so that the ex- 

 ternal form in its earlier condition, is far from uni- 

 form in the families which reckon aquatic types. 

 Among the hymenopterous insects, Bees, Wasps, 

 &c, we have some in which the larvae assume the 

 form of Maggots and Worms, and others in which 

 the larvae assume the form of the higher insects. 

 For instance, in Tenthredo, the larva assumes the 

 form of a Caterpillar. (Plate II., fig. A) But in- 

 stead of having only four pairs of suctorial feet, 

 they have seven. And this is at once an indica- 



