THE LIFE-HISTORY OF A LEPIDOPTEEOUS INSECT. 245 



abdominal segments of the embryo of GasteropacTia quercifolia were at 

 first devoid of appendages, and that when they did appear they de- 

 veloped only on those segments on which they persist in the adult 

 (Morp. Jahrhuch, xiii., 1888, pp. 609-610). This last author also finds 

 the abdomen of the embryo insect to consist of eleven true segments, 

 and he believes that he has found distinct traces of coelomic cavities in 

 the eleventh segment. 



16. On TfiE ORIGIN OF THE BLOOD-TISSUE (BlUTGEWEBe). — The 



important part played by the blood-tissue in larval nutrition, together 

 with the supposition, for many years entertained by certain eminent 

 scientists, that circulation of the blood did not take place in insects, 

 has led to considerable attention being devoted to the subject. The 

 origin of this "blood-tissue " was worked out at consideraljle length in 

 1891 by Graber (" Ueber die embryouale Anlage des Blut- und Fett- 

 gewebes der Insekten." Biol. Centralbl., Bd. ii., Nos. 7-8., pp. 212- 

 221:) and by Wielowiejski. The latter, who approaches the matter from 

 an anatomical point of view, at the same time expresses some general 

 opinions as to the origin of the structures included under this term. 

 He is very careful not to postulate a common origin for all the com- 

 ponent structures of his " Blutgewebe," but includes them under this 

 common term ; Avhilst Graber does not hesitate to conclude that the 

 different tissues comprising Wielowiejski's " Blutgewebe " are genetic- 

 ally related, and from the study of insect embryos, Graber arrives at 

 the following conclusions: — 1. That oenocytes (certain cell-masses) are 

 derived from the ectoderm. 2. That they are metamorphosed into the fat 

 body. 3. Thatthe blood corpuscles arise from the fat body (and also directly 

 from the oenocytes ?). According to Graber therefore all these — oenocytes, 

 fat body, blood-corpuscles, are ectodermic structures, a very bold con- 

 clusion when, as Wheeler says, " we are accustomed to derive the cor- 

 puscles and the connective tissue from the middle germ-layer." 

 Tichomiroff, a Kussian embryologist, described in 1882 (" The em- 

 bryonic development of the Silk-worm {B. mori).'" Pnbl. Labor. Zool. 

 Mas. MoscoH, vol. i.) segmental masses of cells originating from the 

 ectoderm near the stigmata ; whilst Korotneff, another Russian embry- 

 ologist, in 1885 (" Die Embryologie der Gryllotalpa," Zeitsch. f. Wiss. 

 Zool., Bd. xli.) also described these cells. Wheeler, in discussing these 

 articles {Psyche, vol. vi., p. 255 et seq.) considers Graber to be correct in 

 referring the cells described in them to the oenocytes of Wielowiejski, 

 but ascribes the development of the " fat-body " to an entirely different 

 source from that indicated by Graber. The fat-body, according to 

 Wheeler, is a " thickened part of the inner coelomic wall, due to an 

 accumulation of fat-vacuoles in the cytoplasm of the mesoderm-cells." 

 According to Graber it is (as we have said) an accumulation of the 

 embryonic oenocyte cells or those cells which become oenocytes in the 

 larva. Wheeler gives reasons for supposing that there is no connection 

 between these oenocytes and the blood corpuscles, except in so far as 

 they are both " blood-tissue," and concludes that the fat-body (as we 

 have seen above) is not derived from the oenocytes, but is of meso- 

 dermal not ectodermal origin, as indeed has generally been supposed, 

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

 oenocytes. His final conclusions on the origin of the blood-tissue are 

 fully summarised in Psyche, vol. vi., p. 257. 



Wheeler calls attention to the fact that, whereas most insect em- 

 bryos develop and possess these large oenocytic cells, only " the winged 



