A STt'DV OF THE P.LOOD OF CERTAIN COEEOPTEKA. 161 



time of extrusion^ tlie uudig'ested residue becomes increasiugly 

 basic in its staining* i-eactiou. 



On examining with dark background illumination a drop of 

 blood immediately after removal, both forms of cells, phago- 

 cytes and small round cells, which are observed to be very 

 granulai-, are seen to exhibit very numerous fine pseudopodia, 

 about "2 fx in diameter and of length occasionally surpassing 

 that of the cell. No amoeboid movements are seen, but after 

 a time the gi-anules of the protoplasm exhibit Brownian 

 movement, which ultimately ceases when death has occurred, 

 without the cell, however, becoming vacuolated as do human 

 leucocytes. At the time of death the pseudopodia have 

 become somewhat indistinct, their situation being indicated 

 by granules apparently derived from the protoplasm. 



The mode of division of the phagocytes does not always 

 appear to be the same. In Dy tiscus only amitotic division 

 was seen (fig. 5), and that comparatively rarel}^ In Hydro- 

 philus, however, mitotic divisions were faii-ly common (see 

 figs. 15 and 16), but no amitotic forms were met with. It is 

 quite possible, however, that both forms of division occur in 

 the two genera examined, but we have nevertheless been 

 unable to observe either mitotic division in Dytiscus, or 

 amitotic division in Hydrophilus. We have not been able 

 to observe cell-division in the small round-cells.^ 



The oi-igin of the free cells in the blood of insects has been 

 attributed to various sources by different writers. Cnenot 

 (10) and Balbiani (10) derive the leucocytes fi-om the peri- 

 cardial cells. Schaffer (10) derives at least some of these cells 

 from the fat-body cells, but Kowalewsky (10) denies any 

 leucocyte formation to either the pericardial or fat-body cells, 

 asserting that the blood-cells arise from special nests or 

 islands of tissue near the heart. 



' Hollande (loc. cit.),m dealing with other Coleoptera, Coccinella , 

 Mysia and Epilachnia, describes phagocytes similar to, but consider- 

 ably smaller than, those above described. These reproduce by mitosis. 

 The other class of cells which he. described in those species, viz. the " cel- 

 lules a spherules,"' is entirely absent in Dytiscus and Hydrophilus. 

 VOL. 56, HAET 1. NEW SERIES. 11 



