270 GENERAL ANATOMY OR HISTOLOGY OF BLOW-FLY. 



nuclear spindles have been described in the ova, and I have no 

 doubt of their occurrence, 1 have not observed them in any of 

 my preparations. 



The cells of the embryo and of the imaginal discs are so 

 small that they are not favourable objects for the observation of 

 karyomitosis. Large multinuclear cells occur, however, in both 

 the larva and imago in the form of cell-chaplets (see pp. 6i and 

 85), in which the nuclei are undoubtedly undergoing multipli- 

 cation, and in these I have been quite unable to discover 

 nuclear figures. 



Nor, so far as I know, has anyone ever claimed to have 

 observed the phenomena of karyomitosis in these cells. The 

 direct division of the nucleus has been observed by me in the 

 blood corpuscles, leucocytes, of the larva, but under circum- 

 stances unfavourable for the observance of karyomitosis if it 

 occurs (see page 271) ; so that I regard the occurrence of 

 direct division as an open question, but still hold that it is 

 probable. 



2. THE PARABLASTIC TISSUES. 



The tissues or tissue elements traced to the parablast or 

 mesenchyme (see page 235) are the blood corpuscles, the con- 

 nective reticulum which forms the bed in which the tracheal 

 capillaries lie, the fat bodies, the oinocytes, and the multi- 

 nucleated cell-chaplets. Phagocytes are probably merely modi- 

 fied blood cells, but whether all phagocytes are derived from 

 these, or indeed solely from the parablastic tissues, although 

 probable, cannot be positively asserted. 



The Blood Corpuscles are amoeboid cells, measuring from 6 to 

 12" in diameter. They are far more abundant in the resting 

 larva and pronymph than in the imago. In the larva they 

 exhibit resting nuclei, with a single, highly refractive nucleolus 

 and little chromatin. In this stage I have observed the direct 

 division of the cells. The process occupies about half an hour. 

 The nucleus is first withdrawn to one end of the cell (Fig. 17 bis, 

 3a), and a constriction then occurs in the equator of the cell. This 



