TRANSACTIONS OF THE SECTIONS. 125 



similar. If we compared the larviB, this fact became mucli more evident. It had 

 been pointed out by Brauer and also by himself that the two tj-pes of larvaj which 

 Packard had proposed to call tlie eruciform and leptiforui ran through tlie principal 

 groups of insects. This was obviously a fact of great importance. If individual beetles 

 were derived from a form very similar to that of the existing- genus Ccmipodea, it 

 was surelj' no rash h^'pothesis to suggest that the Coleoptera as a group might be 

 so. If he were aslced to describe the insect type, he would say it was an animal 

 composed of head with mouth-parts, eyes, and antennae, a tliorax made ;ip of three 

 segments, each Avitli a pair of legs, and a many-.=egniented abdomen with anal 

 appendages. This, for instance, would describe the larva of a small beetle named 

 Sitaris ; and, speaking generally, it might be said that (excepting the weevils) 

 Coleoptera generally were derived from larvre of this type. The same was also 

 true of Neuroptera, Orthoptera, and Trichoptera. The larva> of Lepidoptera, from 

 the large size of tlie^abdomen, had been generallj', and, as he thought, wrongly, 

 classed with the maggots of tiies, bees, &c. The three thoracic segments were, 

 on the contrary, marked bj^ legs, and, excepting gi'eater clumsiness in general 

 appearance, they essentiallj'- agreed with the type already described. No Dipterous 

 larvffi belonged, however, to this type. Insects, then, widely diflerent in their 

 mature state closely agreed in their larval states. Was there any mature form 

 which also corresponded to the hexapod larvfe of insects ? We need not have 

 been surprised if this tj^pe, through wliich it would appear that insects must have 

 passed so many ages since (for winged Neuroptera have been found in carboniferous 

 strata), had long ago become extinct. But the genus Campodea still represented 

 it. It seemed to him also highly significant that its mouth -parts were intermediate 

 between the haustellate and maudibulate types. There were good grounds, there- 

 fore, for considering the various types of insects to have descended from ancestors 

 more or less resembling the genus Campodea. 



This ancient t3'pe may have been possibly derived from one less highly developed, 

 resembling the modern Tardigrades, such as Macrohiotus. Further still, such 

 genera as Lindia close!}' resembled the vermiform type of larva general in Uiptera 

 and occurring in other groups. There was reason to think that amongst insects 

 the segments preceded the appendages in appearance, which was the reverse of 

 what was the case in Crustacea, although this stage of development might have 

 eluded observation from its trausitoriness. Fritz Miiller and others considered the 

 vermiform type of larva more recent than the hexapod. Considering, however, 

 that the vermiform type was altogether lower in organization and less differentiated 

 than the Campodea (hexapod) form, he considered that the latter was derived from 

 vermiform ancestors; and Nicolas Wagner had shown, in the case of a small gnat 

 allied to Cccidonujia, that these vermiform larvte still, in sonie cases, retain reproduc- 

 tive powers. Such a lar\a very closely resembled some of the Rotatoria, such as 

 Lindia, in which both cilia and legs were altogether absent. lie agreed with 

 Herbert Spencer in regarding this vermiform tj^pe as the result of a modified 

 segmentation. For the next descending stage we must loolc amongst the Infusoria. 

 Other forms of Rotatoria, such as the very remarkable Fedalion discovered last 

 year by Mr. Hudson, seemed to lead to Crustacea through the KanpHiis form. 

 (The ti'ue worms appeared to constitute a separate branch of the animal kingdom.) 



Probably, again, in some such forms as Hackel's Mayosphcera and Protamccba, 

 the primitive ancestors of even such lowly organized types as 3Iacrobiotiis and 

 Lindia must be looked for. And if it were said to be incredible that even the 

 lapse of geological time should have been sufiicient to bridge over the immense 

 interval between such creatures as these and Campodea, or even the Tardigrades, 

 we might consider what happened under our eyes in tlie development of each one 

 of these creatures in the proverbially short space of an insect's individual life. Tlie 

 de^•elopraent of the egg of a Tardigrade went through the same course as the 

 Maffosphcvra ; and from the cells which were the result of the process of yolk- 

 segmentation, the body of the Tardigrade vras built np. Similar processes occurred 

 in tlie development of many other species belonging to most distinct groups. 

 Yolk-segmentation occurred in Entozoa, in Rotifera, Ecliinodermata, Mollusca, and 

 Vertebrata, as was illustrated by the diagrams which were shown. It was true 

 that yolk-segmentation was not universal in the animal ; kingdom but its absence 

 1872. 10 



