486 



second part of this paper, and shall merely remark here that 

 this view is quite untenable. 



The leucocytes of the larva in its first instar are not very 

 numerous; they aro about 5-7ju, in diameter, and like most 

 of the tissue cells at this stage have a fairly hyaline cytoplasm 

 and a clear nucleus containing a large karyosome. They are 

 visible through the transparent cuticle and usually lie very, 

 still. They do not grow in size during larval life. 



Their function during this period is apparently to engulf 

 any bacteria which may have entered the circulation, and I 

 have been able to observe them in young transparent larvae 

 lying quite still in the blood, and absorbing minute bodies 

 (micro-organisms ?) which were floating about in it. They 

 are not, however, called extensively into activity till a little 

 after feeding ceases. At this time the disintegration of 

 larval tissues begins; and although the dead and dying larval 

 cells are not bodily attacked till a day or two later, yet an 

 absorption of their products of degeneration (globules and 

 granules which have failed to dissolve) may occur. This 

 period is marked by a great increase in the number of leuco- 

 cytes, and during the next forty-eight hours their proliferation 

 becomes very extensive. 



At first the leucocytes content themselves with absorbing 

 stray granules and globules cast out by the degenerating 

 cells, but later, especially at the end of the time of pupation, 

 they fall upon the dead larval cells which have not yet dis- 

 appeared and rapidly remove them. The process has been 

 described above in the various tissues and need be only 

 briefly mentioned here. As a rule, it seems, the leucocytes 

 do not enter the cells which they are attacking, as occurs so 

 markedly in Calliphora, but, attaching themselves to their 

 walls, send in a pseudopod, which gradually spreads out 

 within the disintegrated cell, and an absorption of its sub- 

 stance commences (fig. 129). It is only rarely in Nasonia that 

 a leucocyte bodily enters the larval cells. At other times the 

 leucocytes content themselves with nibbling off small pieces 

 of tissue, which accumulate in small rod-like or rounded 

 structures within their cytoplasm (fig. 195) ; at times, how- 

 ever, a leucocyte may tear off long shreds of tissue. So large 

 may these be that, to be accommodated within the leucocyte, 

 they have to be bent and twisted about (figs. 197, 199). 



Division of the leucocytes appears to be only by binary 

 fission. At times fully gorged leucocytes divide; but the 

 engulfed food always descends to only one of the resulting 

 cells (fig. 196). I could not observe any cases of mitotic 

 division. 



