THE IXSECTS DERnTBD FROM THE AVORJIS. 157 



originally from the same early crustacean resembling the larva 

 of a crab or shrimp, that the diflereuces between the two types 

 are too great, or, in other words, the homologies of the two 

 classes too remote,* and the two types are each too specialized 

 to lead us to suppose that one was derived from the other. 

 Moreover, we find through the researches of Messrs. Hartt and 

 Scudder that there were highly developed insects, such as May 

 flies, grasshoppers, etc., in the Devonian rocks of New Bruns- 

 wick, leading us to expect the discovery of low insects even iu 

 the Upper Silurian rockSi At any rate this discovery pushes 

 back the. origin of insects beyond a time when there were true 

 Zoeaj, as the shrimps and their allies are not actually known to 

 exist so far back as the Silurian, not having as yet been found 

 below the coal measures. 



The view that the insects were derived from a Zoiia was also 

 sustained by Friedrich Brauer, the distinguished entomologist 

 of Vienna, in a paper f read iu March, 18G9. Following the 

 suggestion of Fritz Miiller and Ilaeckel, he derives the ancestry 

 of insects from the Zoea of crabs and shrimps. However, he 

 regards the Podurids as the more immediate ancestors of the 

 true insects, selecting Campodea as the type of such an ances- 

 tral form, remarking that the " Campodea-stage has for the 

 Insects and Myriopods the same value as the Zoea for the 

 Crustacea." He says nothing regarding the spiders and mites. 



At the same time J the writer, in criticising Haickel's views 

 of the derivation of insects from the Crustacea (ignorant of 

 the fact that he had also suggested that the insects were possi- 

 bly derived directly from the worms, and also independently of 

 Brauer's opinions) declared his belief that though it seemed pre- 

 mature, after the discovery of highly organized winged insects 



* The Zoea is born with eight pairs of jointed appendages belonging to the head, 

 and with bo tlioracic limbs, wliile in insects there are but four pairs of ceplialic 

 appendages and three pahs of legs. Correlated with tliis difference is the entirely 

 different mode of grouping the body segments, tlio head and thorax being united 

 into one region in the crab, hut separate in tlie insects, the body being as a rule 

 divided into a head, thorax and abdomen, while tliese regions are much less dis- 

 tinctly marked in the crabs, and liable in the different orders to great variations. 

 Tlie great differences between the Crustacea and insects are noticeable at an early 

 period in the egg. 



t Considerations on the Transmutation of Insects in the Sense of the Theory of 

 Descent. Kead before the Imperial Zoological-botanical Society iu Vienna, April 

 3, 1SC9. 



t American Naturalist, vol. 3, p. 45. March, 1869, 



u 



