234 



PSYCHE. 



[March 1S92. 



dency to fuse with one another. 



The size of the oenocytes in a given 

 species appears to vary directly as the 

 age of the insect. This is shown by the 

 following measurements : 



cytoplasm. nucleus. 



Xiph. ensiferum \ 



embryo-revolution I iija 7-9 fj. 



£ completed. J 



Xiph. ensiferum "I ->fi - 



hatching J - ••!> r 



Xifh. fasciatum \ 



larva 10 mm. long J 



Xiph. ensiferum \ 



adult. J 



33-51* 

 37 V- 



nji 



iiji 



12-13H 



Not only do these measurements 

 show a gradual increase in both cyto- 

 plasm and nucleus, but they also show 

 that the cytoplasm grows relatively 

 somewhat more rapidly than the 

 nucleus. 



Ephemeridea. Fig. 4 represents 

 the pleural portion of a section through 

 one of the abdominal segments of a 

 nearly mature Blasturus nymph. Nearly 

 the whole of that portion of the pleural 

 hypodermis which is included between 

 the insertions of the tergosternal, or res- 

 piratory muscles, is seen to consist of 

 oenocytes. The hypodermal cells proper 

 are reduced to small chromophilous 

 elements filling the interstices between 

 the large clear adenoid cells and cover- 

 ing them with a thin layer externally. 

 That the oenocytes are really still com- 

 pletely imbedded in the hypodermis and 

 do not protrude freely into the body- 

 cavity is apparent from an examination 

 of their inner surfaces, where traces of 

 the inner ends of the hypodermal cells 

 still persist as plates of protoplasm. 



When the abdomen is slit sagittally and 

 spread out, the pale oenocytes are seen 

 to line the pleural angles of the segments 

 as an even pavement-like layer. The 

 area covered by these cells is so large that 

 the metameric masses are interrupted 

 only by the constrictions separating the 

 segments. In the first abdominal seg- 

 ment the oenocytes are heaped up into 

 a mass instead of forming a single layer. 

 It may be further noted that the stig- 

 matic trunks of the abdominal tracheae 

 pass into the gills at the posterior edges 

 of their respective segments, so that the 

 oenocyte clusters lie in front of the stig- 

 mata. This is the reverse of their posi- 

 tion in the embryos of Orthoptera, Col- 

 eoptera and Lepidoptera and were it 

 not that the insect under consideration 

 was nearly mature, we might doubt 

 whether the position of the oenocyte 

 clusters with respect to the tracheae was 

 of much morphological significance. 

 On the other hand the oenocytes of 

 Blasturus certainly show a very embry- 

 onic condition in that they are still im- 

 bedded when the insect is practically 

 mature in the hypodermis from which 

 they differentiated. 



The separate oenocytes measure 15 

 — 23H in diameter ; their nuclei 7 n. 

 They are perfectly distinct on the one 

 hand from the blood corpuscles which 

 measure only 3.5 (* and on the other 

 from the fat-body. 



In the nearly adult nymph of a very 

 different species (an Ecdyurus-like 

 form, probably the same as the one fig- 

 ured in Eaton's monograph PI. 59) the 



