222 A'. Ooi/nia: 



spot where th eterminal gill lamellae pass over into the rectal epitheliiim. 

 'l'hese cells have the nuclei niore or less spindle shaped of elongate form 

 usually niiich larger than those of branchial cells. These cells are 

 probably the indifferentiated cells destined to be converted afterwards into 

 the connective tissue, and they are exactiy similar to the cells found 

 beneath the rectal epithelium (tpi. Or, in other words, they have come 

 out of their original positions throiigh the wounds of the epithelium resulted 

 from the ecdysis of gills, to form the connective tissue under the newly 

 formed epithelium inei. Leucocytes and pigment granules imbedded in a 

 protoplasmic fragment or some of the branchial cells are also to be seen 

 together with these cells. 1 have often observed that some cells of the 

 branchial epithelium are crowded just beneath the nevv epithelium, mingled 

 u'ith the connective tissue cells described. but they make by no means 

 a permanent tissue, but are absorbed sooner or later probably by leucocytes, 

 leaving pigment granules behind. 



Significance of Falling off of the Epithelial Cushion. 



That the rectal gills correspond to rectal glands or at least to a 

 part of them in other insects has been considered by previous authors 

 to be very probable. I also incline to this view after observing the glandulär 

 nature of the cushion cells as above mentioned. Still remains obscure. 

 the question, why the cushion cells must fall off in the course of 

 metamorphosis, from other parts of branchial epithelium. However from 

 the accounts given obove it is clear that the detachment of the epithelial 

 cushion causes the destruction of epithelial arrangement of cells, and 

 subsequently makes path through which the germinal cells of connective 

 tissue would come forth, unless these cells beneath the epithelium are 

 not able to wander out. On the basement membrane of the gills are for 

 some time to be found such germinal cells, but I cannot say with certainty, 

 whether it happens so invariably or not. 1 believe that some of these 

 cells would be detected by a closer Observation on the basement membrane; 

 they form probably a part of supporting tissue under the new epithelium. 

 If this be the case, the significance of the falling off of epithelial cushion 

 Iwould become far clearer than before. 



Fat cells in the Basal Cushion. 



Here I shall touch briefly upon the nature of cells or tissue filling 

 up the Space of the basal parte of a gill or the basal cushion. These 

 cells or tissue, generally known as the fat cells or the fat tissue, have 

 already been described by Chun (1876) and Sadones (18061 in Lihelliila 

 depressa, and also by Faussek (1887i and by Sadones (1896i in some of 

 Aeschna. It has been considered, at the same time, that these cells 

 are very distinct in their nature as compared with the ordinary fat cells or 

 adipose tissue in other parts of the insect body; each cell has a large 

 roundish nucleus which is always found near the centre of the cell (fig: 

 15); the cell contents show a fine granulär appearance. but with no fat 



