THE LEPTUS AND NAUPLIUS FORMS COMPARED. 159 



Woodiana, while the Devonian insects described from St. John 

 by Mr. Scudder, are nearly as highly organized as our grass- 

 hoppers and May flies. Dr. Dawson lias also discovered a well 

 developed milleped (Xylobius) in the Lower Coal Measures of 

 Nova Scotia ; so that we must go back to the Silurian period in 

 our search for the earliest ancestor, or (if not of Darwinian 

 proclivities) prototype, of insects." 



Afterwards* the writer, carrying out the idea suggested above, 

 "referred the ancestry of the Myriopods, Arachnids, and Hex- 

 apodous insects to a Leptus-like terrestrial animal, bearing a 

 vague resemblance to the Nauplius form among Crustacea, inas- 

 much as the body is not differentiated into a head, thorax and 

 abdomen [though the head may be free from the rest of the 

 body] and there are three pairs of temporary locomotive appen- 

 dages. Like Nauplius, which was first supposed to be an adult 

 Entomostracan, the larval form of Trombidium had been de- 

 scribed as a genus of mites under the name of Leptus (also 

 Ocypete and Astoma) and was supposed to be adult." 



In the same year Sir John Lubbockf agrees with Brauer that 

 the groups represented by Podura and Campodea may have been 

 the ancestors of the insects, remarking that "the genus Cam- 

 podea must be regarded as a form of remarkable interest, since 

 it is the living representative of a primaeval type from which 

 not only the Collembola (Podura, etc.) and Thysanura, but the 

 other great orders of insects, have all derived their origin." 



The comparison of the Leptus with the Nauplius, or pre-Zocal 

 stage of Crustacea, is much more natural. But here we are met 

 with apparently insuperable difficulties. While the Nauplius 

 (Fig. 191) has but three pairs of appendages, which become the 

 two pairs of antennae and succeeding pair of limbs of the adult, 

 in the Leptus as the least number we have five pairs, two of 

 which belong to the head (the maxillae and mandibles) and three 

 to the thorax ; besides these is a true head, distinct from the 

 hinder region of the body. It is evident that the Leptus funda- 

 mentally differs from the Nauplius and -begins life on a higher 

 plane. We reject, therefore, the Crustacean origin of the 

 insects. Our only refuge is in the worms, and how to account 



*In a communication made to tlie Boston Society of Natural History, Oct. 17, 

 1870 (see also "American Naturalist" for Feb. and Sept., 1871). 



fOn the Origin of Insects, a paper read before the Linna^an Society of London 

 Nov. 2, 1871, and reported in abstract in "Nature," Nov. 9, 1871. 



