A STUDY OF THE JILOOD OF CERTAIN COLEOPTEEA. 163 



and Hydrophilus by phagocytes and small round-cells. In 

 the phagocytes of Dytiscus fragmentation of the nucleus 

 occui-s, which is comparable to that seen in polynuclear 

 leucocytes. 



Turning now to points of difference, the low osmotic 

 pressure of the blood of Dytiscus and Hydrophilus, repre- 



M M . • 



sented by a - to - (undissociated) solution, contrasts with 

 23 28 



M 

 that of mammalian blood, represented by a— (dissociated) solu- 

 tion. A more striking point of difference is the absence of 

 cells containing haemoglobin in the blood of the former^ 

 which is also free from dissolved hfemoglobin. Moreover, the 

 white cells in Dytiscus and Hydrophilus are scanty, 

 relatively to those of mammalian blood ; no oxyphile granules 

 can be recognised in the phagocytes when fixed and stained 

 by Leishman's method, nor are platelets present. Mitoses are 

 not uncommon in the phagocytic cells of Hydrophilus. In 

 both Dytiscus and Hydrophilus no spontaneous coagula- 

 tion of the blood occurs on standing. In both insects oxygena- 

 tion appears to occur by direct transfer to the tissues of 

 oxygen supplied by the tracheal vessels, the blood-plasma not 

 serving as a medium of exchange. 



Literature. 



1. Landois, M. — " Beobaclitimgen iiber das Blut der Insekten," ' Zeit. 



f. wiss. Zool.; 1864, Bd. xl, S. 55. 



2. Cattaiieo. — " Sulla morpliologia delle cellule amceboidi dei Mol- 



lusclii e Artropodi." " Boll. Sci. Pavia." 1889. v. 11. 



3. Wagner, W. A. — " Uber die Form der korperliclien Elemente des 



Blutes bei Artliropoden, etc.," 'Biol. Centralbl.,' 1890, Bd. x, 

 S. 428. 



4. Cuenot, L. — " Etudes sur le sang et les Glandes Lympliatiques dans 



la Serie Aniniale," ' Archives de Zoologie exp.,' 1891, t. 9, p. 13. 



5. Durham, M. E. — " On Wandering Cells, more especially in regard 



to Excretory Functions," 'Quart. Journ. Micr. Sci.,' 1892, vol.33, 

 p. 81. 



