162 J. 0. WAKKLIN TiARRATT AM> (iEOROK AKNoLD. 



Our own observations do not permit us to make any con- 

 fident statement as to the origin of the blood-cells from any 

 of the tissues of the body. It appears to iis, however; that 

 the evidence adduced in fnvoiir of the above sng-g-ested modes 

 of origin is altogether inadequate, for both the pericardial and 

 fat-body cells are torally different in aspect from the blood- 

 cells. 'J'hus the pericardial cells of Dytiscus and Hydro- 

 philus are considerably larger than the largest blood-cell;, and 

 their nuclei are relatively smaller, while their cytoplasm is 

 very abundant. Again, if the blood-cells arose from any of 

 the above sources, transitional forms would be present ; these 

 we have failed to observe. 



On the other hand, whatever other mode of origin of the 

 blood-cells may exist, it is clear, since division figures occur 

 in Hydrophilus and Dytiscus (mitotic and amitotic), that 

 the supply of these cells is kept up, in part at any rate, by 

 multiplication in tlie blood-plasma. 



CoMPAKISON WITH ]\lAMMA],rAN BlOOD. 



In the above investigation we have applied the term " blood" 

 to designate the circulating fluid of Coleoptera. This fluid 

 presents, however, several important points of difference from 

 the blood of the higher mammalia. It will, therefore, be of 

 advantage briefly to conti-ast the characters of these two fluids 

 so far as the present limitations of knowledge permit a com- 

 parison to be made. 



The blood of Dytiscus and Hydrophil us resembles mam- 

 malian blood in so far as it consists of an albuminous fluid 

 containing cells. The fluid part resembles mammalian blood- 

 plasma in containing proteid, coagulable by heat. Whether 

 more than one form of heat-coagulable proteid is present can- 

 not as yet be stated, but it may be observed that a globulin 

 precipitable by dilution with distilled water, and therefore 

 held in solution by the saline constituents of the fluid, is also 

 present as in mammalian blood. The cellular elements of 

 mammalian blood are represented in the blood of Dytiscus 



