EUPAGTTRTJS. 521 



which the outer afferent vessels of the gill lamellae 

 communicate runs ventrally the length of the thorax. 

 This Sternal sinus is continuous with the cavity of the 

 abdomen, which constitutes one great Abdominal sinus. 

 The sternal sinus does not communicate directly with the 

 gills, but is connected to the Infra-branchial sinuses on 

 each side of the body, into which the gill vessels open — 

 by five distinct clefts on either side — the Branchial 

 sinuses. Into, the infra-branchial sinuses also open the 

 haemal cavities from the thoracic limbs. 



The Afferent Branchial veins, mentioned above, run 

 from the infra-branchial sinus up the outer side of 

 each gill. The blood is conducted down the inner side of 

 the gill lamellae by the Efferent Branchial veins to the 

 five Branchio-cardiac veins, which open by three slits on 

 each side into the pericardium. 



The Blood is a slightly opalescent but almost trans- 

 parent fluid in which corpuscles float. The presence of 

 haemocyanin gives it a faint bluish colour, which 

 becomes intensified if the blood be left exposed to air. 

 It coagulates under such conditions to a grey -white solid. 

 The setting is effected by clear amoeboid cells which 

 float in the lymph. Several kinds of cells (or 

 amoebocytes) are to be found in the blood, but, 

 according to Cuenot,* they constitute a series of stages 

 in the breaking down of one kind only. The principal 

 amoebocytes are semi-transparent amoeboid cells with 

 large nuclei and finely granular cytoplasm. These cells 

 increase in size and become full of eosinophilous granules. 

 The almost solid body of granules is a prominent object 

 in the blood at this stage, and amoebocytes in this 

 condition are known as eosinophilous amoebocytes. The 



* Archives de Biologie, T. XIII, 1895, p. 245. 



