2 8o ANIMAL BIOLOGY. [Part II. 



at the bottom of which is a layer of paraffin, poured in liquid 

 and allowed to set. The worm should be pinned out with the 

 first twenty-eight segments well stretched out, and the segments 

 should be numbered by marking the paraffin at the fifth, tenth, 

 fifteenth, and twentieth rings. The body should be opened by 

 a median incision from the twenty-fifth to the second segment. 

 Care must be taken not to cut so deeply as to injure the blood- 

 vessels. It will now be seen that the external constrictions 

 between the rings answer to internal septa which divide the 

 body into as many compartments as there are rings. These 

 must be carefully divided near the body-wall on each side, and 

 the walls pinned out laterally so as to display the internal 

 organs, as seen in Fig. 84, A., which represents the anatomy of 

 a sexually mature worm. After the worm is thus opened up 

 under water, the water should be poured away and replaced 

 with spirits of wine, which enables some of the parts to be more 

 readily seen, and hardens some of the organs so as to render 

 their dissection more readily accomplished. 



The digestive canal is seen in the middle line with buccal 

 cavity (b. c.) anteriorly, opening into a large pharynx (ph.), 

 from which fine muscular fibres stretch to the body-walls. The 

 pharynx is succeeded by a long (esophagus (as.), upon which are 

 three white protuberances in the tenth and twelfth segments. 

 These are the cakiferous glands (c. g.). In the fifteenth ring the 

 oesophagus expands into a crop (cr.), which is followed by a 

 muscular gizzard (gi.) ; after which the intestine (int.) is carried 

 to the end of the body. If a living worm, selected for its trans- 

 lucency, be held up to the light, the intestine will be seen to 

 have a slightly coiled course, except when the worm is elongated 

 almost to the point of rupture. The intestine, in Fig. 84, is cut 

 at the twenty-second ring, and turned back to show the nerve- 

 chain (n. ch.\ which is median and ventral in position. The walls 

 of the intestine are covered with soft yellowish-brown tissue. 



Along the dorsal line of the alimentary canal runs a dorsal 

 blood-vessel, filled with red fluid. This gives off lateral vessels, 

 which in the sixth to the twelfth segments are much enlarged, 

 giving rise to the so-called hearts (h.). 



