April 1S9?.] 



PSYCHE. 



257 



greater portion of the mesoderm of 

 the segment, though this is difficult to 

 decide. It is apparently the earliest 

 organ to differentiate from the walls of 

 the coelomic sacs. Its cells, at first 

 wedge-shaped, gradually increase in 

 size, become rounded and highly vac- 

 uolated and resemble the fat-bodv ele- 

 ments, from which they may, neverthe- 

 less, always be distinguished by their 

 peculiar yellow tint. I have traced 

 the organ, which is a definite circum- 

 scribed structure, and which I call, for 

 the present, the suboesophageal body, 

 through the embryo into the larva, 

 where it disintegrates and finally 

 disappears. I regard it therefore, a s 

 a truly embryonic and early larval 

 structure, quite distinct, at least physio- 

 logically, from the fat-body. Its func- 

 tion is very doubtful. If the trito-cere- 

 bral segment is homologous with the 

 second antennary segment of the Crus- 

 tacea and if, moreover, the suboesopha- 

 geal body really develops from the 

 mesoderm, it may be the homologue of 

 the l ' green-gland " and consequently 

 nephridial in its nature. 



Reserving a general consideration of 

 the "blood-tissue" for future publi- 

 cation, I here conclude with a brief 

 summary of the points brought out in 

 the foregoing paragraphs : — 



(i) The fat-body of the Insecta is 

 derived from the mesoderm — being a dif- 

 ferentiation of portions of the coelomic 

 walls and therefore metameric in 

 origin. 



(2) The oenocytes are derived by 

 delamination or immigration from the 



ectoderm, just caudad to the tracheal 

 involutions. They are also metameric 

 organs. 



(3) They are limited to the eight 

 trachigerous abdominal segments. 



(4) They appear to be restricted to 

 the Pterygota, in all the members of 

 which group they probably occur. 



(5) They give rise neither to the 

 fat-body nor to the blood but represent 

 o rga n s s u i gen e r is . 



(6) After their differentiation from 

 the primitive ectoderm they never di- 

 vide but gradually increase in size. 



(7) The blood-corpuscles of these 

 insecta appear to arise early in em- 

 bryonic life and perhaps also in post- 

 embryonic life from undifferentiated 

 mesoderm cells. The evidence of the 

 derivation of the blood-corpuscles from 

 the fat-body as such is unsatisfactory. 



(S) The suboesophageal body 



arises in the trito-cerebral segment ap- 

 parently from the mesoderm. Though 

 it resembles the fat-bodv it must be re- 

 garded as a distinct organ. It disap- 

 pears during larval life. 



Clark University, Dec. 22, 1S91.* 



*Since the above article was written and sent to 

 "Psvche," I have received two publications bearing 

 on the origin of the fat-body in the insect embryo. The 

 first is an account published in the second part of Kor- 

 schelt and Heider's Lehrbuch der vergleichenden ent- 

 wicklungsgeschichte der wirbellosen thiere, of Hey- 

 mons' studies on Phyllodromia germanica. Soon after- 

 wards Dr. Heymons kindly sent me a copy of his in- 

 teresting paper (Die entwickluns: der weiblichen ges- 

 chlechtsorgane von Phyllodromia (Blatta) germanica 

 L. Zeitschr. f. wiss. zool. LIII. 3. 1S91, p. 434-536) the 

 lucid illustrations of which show essentially the same 

 method of origin for the fat-body as fig. 3 in my plate. 

 He finds, also, that other portions of the coelomic wall 

 may contribute to the formation of the corpus adiposum.) 



