226 ELEMENTARY BIOLOGY. [CHAP. 



trunk at the base of eye-stalk, and distributed to 

 the antennule and rostrum. 



8. The re?ial arteries ; two or more branches break- 

 ing up on the anterior face of the green gland. 

 £. Other minor branches, which are variable. 



4. Puncture any one inter-sternal membrane of a freshly- 

 killed animal ; blood will escape freely (a blood space 

 has been entered). Treat the inter-articular mem- 

 brane between the two last thoracic sterna similarly; 

 insert the point of a cannula and inject. 



a. Remove the branchiostegite and examine the 

 branchiae. The injection will have filled some of 

 the afferent branchial vessels ; large trunks running 

 (one for each gill) along the outer face of the stem 

 externally to the efferent vessel (§ I. b.). 



b. Make a transverse section across the thoracic region. 

 With a little care the afferent branchial vessels can 

 be traced to a great ventral sinus (sternal sinus) 

 now largely injected. It is in free communication 

 with the adjacent blood-spaces. 



5. The blood. Obtain a drop of blood, from a freshly- 

 killed Crayfish and examine under a high power. 



a. The plasma ; colourless. 



b. The corpuscles ; colourless and amoeboid, each with 

 a large round nucleus. Their pseudopodia ; fili- 

 form and frequently very numerous. 



Watch their movements ; they exhibit a great 

 tendency to run together into aggregates prior to 

 disintegration, upon exposure, after removal from 

 the body. 



