22 URITISH LEPIDOPTERA. 



insects, has led to considerable discussion. The origin of the "blood- 

 tissue " was worked out at length by Graber, who concludes that the 

 whole of the structures forming this " tissue," viz., oenocytes (certain 

 cell-masses), fac-body and blood-corpuscles, are ectodermic structures. 

 He further finds that the oenocytes are metamorphosed into the fat- 

 body, and that the blood corpuscles arise from the fat-body, and, 

 probably, also directly from the oenocytes. Wheeler, f however, looks 

 upon the fat-body as a thickened part of the inner coelomic wall, 

 due to an accumulation of fat-vacuoles in the cytoplasm of the 

 mesoderm-cells." He further concludes that the fat-body is not derived 

 from the oenocytes, is of mesodermal, not ectodermal, origin, and 

 concludes that there is no evidence for the origin of the blood from 

 the oenocytes. Wheeler also remarks that " Few insects appear to 

 be better adapted for tracing out the origin of the oenocytes than 

 the Lepidoptera. This is especially true of the larger Bombycid moths. 

 That the segmental cell-clusters arise by delamination from the ecto- 

 derm was conclusively made out in the embryos of Platytamia cecropia 

 and Telea polyphemus. Each cluster is several cell-layers in thickness, 

 and lies just behind, and a little ventral to, an abdominal stigma. 

 The succulent cells constituting the cluster are at first polygonal 

 from mutual pressure, but, as the time for hatching approaches, they 

 become rounder and more loosely united. I have not traced them 

 through the larval stages, and merely record these fragmentary obser- 

 vations because they completely confirm Tichomiroff 's and Graber's 

 observation on the origin of the oenocytes from the ectoderm." 



The study of the lepidopterous embryo has given us many other 

 interesting morphological particulars. Kowalewski found ten ab- 

 dominal somites in the embryo of Swerinthus populi, all bearing pro- 

 legs ; whilst Tichomiroff detected eleven abdominal somites in the 

 embryo of Bombyx mori, all provided with prolegs except the first. 

 Graber also found the abdomen of the lepidopterous embryo to consist 

 of eleven true segments, and observed that the abdominal segments of 

 Eutnchd (Gastropacha) quercifolia were at first devoid of appendages, 

 and that, when they did appear, they developed only on those seg- 

 ments on which they persist in the adult. 



The mode in which the earliest development of the generative 

 organs in the embryo of insects takes place is very obscure, but it 

 would appear that the primitive ovaries are composed of a mass of 

 cells, produced by an infolding of the ectoderm. Some writers, 

 however, consider them to be derived from the mesoderm, whilst 

 others trace their origin back to certain so-called pole cells, which 

 originate even before the blastoderm is formed. However this may be, 

 it would appear that they are, in that early stage, quite indistinguish- 

 able from the other blastoderm cells. As development proceeds, the 

 great mass of cells become differentiated into various structures, which 

 subserve a special purpose, or perform a certain function. Certain 

 cells in the ovary, however, retain their primitive condition, and, with 

 it, the power, under suitable conditions, of forming another in- 

 dividual of the same species. On this subject, Woodworth writes : 

 " About the time of the completion of the blastoderm, the already 



* " Ueber die embryonale Anlage des Blut- und Fett-gewebes der Insekten," 



BioL Centralbl., Bd. ii., Nos. 7-8, pp., 212-224. 



f Psyche, vol. vi., p. 255 et. seq. 



