152 J. 0. WAKELIX BARRATT AND GEORGE ARNOLD. 



from five specimens (in April) was found to measure 1"6 c.c. 

 (average amount '32 c.c. from each) ; later in the same month 

 three specimens yielded '43 c.c. (average amount '14 c.c. from 

 each) ; on another occasion (in July) "26 c.c. per specimen was 

 obtained. 



From Dytiscus the average amount obtainable was "10 

 c.c. As affording some idea of the range observable the 

 following data may be given : '42 c.c. obtained from three 

 specimens in February (average amount *14 c.c. from each) ; 

 *375 c.c. obtained from six specimens also in February 

 (average amount *063 c.c. from each) ; 1"3 c.c. obtained from 

 twelve specimens in Marcli (average amount '108 c.c. from 

 each) ; 1'65 c.c. obtained from seventeen specimens in April 

 (average amount "10 c.c. from each). 



The blood was found on centrifugalisation to consist partly 

 of fluid and partly of suspended material. The latter was 

 variable in different animals, but Avas relatively small both in 

 Hydrophilus and in Dytiscus, amounting in the observa- 

 tions made to about 1 per cent, (by volume) of the blood. 



The suspended material consisted partly of cells, partly of 

 free granules. The latter are described in detail below in 

 connection with the blood-plasma ; the former are taken in 

 the succeeding section. The cells formed a relativel}- small 

 amount of the precipitate obtained on centrifugalisation, but 

 owing to the circumstance that the two constituents of the 

 precipitate cannot be separated, no quantitative comparison 

 of the two could be made. 



Characters of the Blood-Plasma of Dytiscus Marginalis. 



Colour and Spectroscopic Appearance. — The blood- 

 plasma immediately after removal was, in a layer four 

 millimetres thick, of a deep amber colour, subsequently 

 changing at the surface of contact with the air to dark brown, 

 almost black (well seen when the blood was kept in a narrow 

 pipette, the upper layer of liquid becoming deeply coloured, 

 while that below, where access of air was prevented, remained 



