262 ELEMENTARY BIOLOGY. [CIIAP. 



vessels ; for the study of these recourse must be had 

 to transverse sections. (Cf. Sect. G. y.) 



d. The blood fluid. Lay open, higli and dry, the 

 body cavity of a freshly-killed worm, and introduce 

 a fine capillary tube into one of the larger vessels. 

 Transfer the drop of red blood thus obtained to a 

 slide, cover and examine at once under a high 

 power. Note — 



a. The blood serum^ a watery ycllowIsh-red fluid in 

 which float 



/5. minute colourless corpuscles. In shape, they are 

 somewhat irregular (rarely oval); each usually 

 contains a central dark granule. 



If unsuccessful by the above method, remove 

 a small portion of one of the larger vessels en 

 masse between two pairs of forceps ; transfer to 

 a slide and allow the fluid contents to escape. 



C;. The nervous system. 



Dissect an entire worm from above, removing the dorsal 

 portion of the body wall, and the alimentary canal from the 

 pharynx backwards. Pin down, wash until (^uite clean, and 

 dissect under water. Examine under a lens and note — 



a. The supra-asophagcal ganglia; two pear-shaped 

 masses lying in the third segment in a depression 

 between the buccal-sac and pharynx. (Cf. Sect. 

 D. I. b.) Fibres can be traced from them to the 

 circum-oral integument. 



b. The circu}nocsophagcal covunissurcs ; seen, on dis- 

 placing the pharynx to one side, to arise from a. 

 The nerves arising from them are distributed — 

 externally, to the first two segments — internally, to 



