vn PRACTICAL DIRECTIONS 389 



4. Note the branch iocardiac veins on the inner side of the 

 thoracic wall. Blow air or inject French blue (see p. 99) 

 into the cut bases of the gills removed, and note that the 

 branchiocardiac trunks extend upwards to the pericardial 

 sinus (see below) from the gills. 



C. General Dissection. 



Holding the animal in your left hand, insert a scalpel 

 carefully beneath the hinder edge of the carapace on the 

 dorsal side, so as to separate the exoskeleton from the soft 

 integument, and then with the large scissors cut along the 

 outer side of each branchio-pericardial groove, and remove 

 the median portion of the carapace. Note the pigmented 

 integument and then remove it, when some of the nearly 

 colourless blood will ooze out. 



1. i. Examine a drop of blood under the microscope, 

 adding salt-solution. Note the nucleated amreboid corpuscles. 

 Sketch. 



2. The pericardial sinus will now be exposed, containing 

 the heart with three pairs of valvular ostia (only the dorsal 

 ostia can be seen at present), through which the blood enters 

 the heart from the pericardial sinus. 



Inject some French blue into the heart through one of 

 the ostia, so as to fill the arteries (tying is unnecessary). 

 Then remove the dorsal part of the exoskeleton and integu- 

 ment bit by bit, all along the thorax and abdomen, as well 

 as the pair of longitudinal extensor muscles lying just beneath 

 the dorsal integument of the abdomen. Pin down under 

 water, dorsal surface uppermost, and note : 



3 . The absence of a continuous muscular layer in the body- 

 wall and of a true crelome, and the presence of irregular 

 spaces (blood sinuses) between the viscera and muscles. 



4. The delicate arteries arising from the anterior and 

 posterior ends of the heart : a, the anterior median oph- 

 thalmic arterv, running forwards to the eye-stalks ; b, the 

 paired antennary artery, on either side of a, and passing 

 forwards and downwards to supply the gizzard, renal organ, 

 feelers, &c. ; c, the hepatic artery (also paired), rather further 

 back and more ventral, extending into and supplying the 

 digestive gland ; d, the median dorsal abdominal artery, 

 arising from the posterior end of the heart, and running 

 along the dorsal side of the intestine, giving off branches in 

 each metamere ; e, the sternal artery, arising just beneath 

 the anterior end of d, and passing directly ventralwards to 

 one side of the intestine (this will be seen better later on : 



PRACT. ZOOL. C C 



