March 1S92.] 



PSYCHE. 



235 



oenocytes are very similar to those of 

 the Blasturus nymph. They measure 

 13-14. 5K- — their nuclei I2H. In this 

 species also the difference in size be- 

 tween the oenocytes and the blood-cor- 

 puscles is very great. There is nothing 

 whatever to indicate that the latter 

 originate from the former. 



Very different is the condition of the 

 oenocytes in the mature nymph of 

 Hexagenia. Here they maybe detected 

 only with considerable difficulty in the 

 pleural fold between the insertions of 

 the respiratory muscles as a few scat- 

 tered cells, differing only in size and 

 clearness from the hypodermal cells in 

 which they are imbedded. 



Odonata. In the nymph of an Agri- 

 onine species of this group oenocytes 

 were detected after considerable search. 

 They are present in clusters consisting 

 of a very few small elements (cytoplasm 

 12-14 n ; nucleus 4.5 p.) imbedded, as 

 usual, in that portion of the pleural 

 hypodermis which is included between 

 the insertions of the tergo-sternal mus- 

 cles. They seem not to be completely 

 covered over by the hypodermis but to 

 project into the body cavity. Their 

 greater size and pale color distinguish 

 them from the hypodermal cells. 



Plecoptera. In a beautiful black 

 and yellow Perlid larva (perhaps an 

 Acroneura) the oenocytes are quite as 

 inconspicuous as they are in the Odo- 

 nata. The specimens studied in section 

 were young, measuring only 6 mm, 

 whereas the mature larva of this same 

 species measures fully 25 mm. Each of 

 the metameric clusters consists of from 



5-6 cells and these are imbedded in the 

 hypodermis surrounding the occluded 

 stigmata. They measure 1S.5 k- ; their 

 oval nuclei up. In their affinity for 

 stains they differ but slightly from the 

 hypodermal cells. 



The imago of a small unidentified 

 Perlid presented very different condi- 

 tions, oenocyte sbeing present in great 

 numbers and distributed through the 

 abdomen and thorax. They lie in 

 niche-like excavations in the hypo- 

 dermal wall, either singly or in groups. 

 Sometimes they appear to form syncy- 

 tia. They vary considerably in size 

 (cytoplasm 14-55H; nucleus 5-30^). 

 The nucleus contains a nucleolus — 

 the only case in which I have found 

 nucleoli in the oenocytes. Compared 

 with their homologues in other forms 

 these cells stain very deeply in borax 

 carmine. 



Corrodentia. The bright yellow 

 oenocytes of Psocus venosus (imago) 

 are massed in metameric clusters about 

 the stigmata. The cytoplasm measures 

 about 1S.5 h- in diameter; the nucleus 

 6 ja. They are not imbedded in the 

 hypodermis, though they lie in contact 

 with it. 



The fat-body which stains very in- 

 tensely in Delafield's haematoxylin and 

 is loaded down with minute urate con- 

 cretions, extends with hardly any in- 

 terruption through the whole body — 

 from the cavity in front of the brain to 

 the terminal abdominal segments. The 

 pericardial fat-body is well developed 

 and very distinct from the fat-body 

 proper. 



