vii PRACTICAL DIRECTIONS 389 



4. Note the branchiocardiac 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 up- 

 wards 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 pig- 

 mented 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 amoeboid 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 integument 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 cceloine, 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 ophthalmic artery, 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 diges- 

 tive 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 ; c, the sternal artery, 

 arising just beneath the anterior end of d, and passing directly ventral- 

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

 compare Figs. 93 and 94) : it perforates the ventral nerve-cord, and 



