4 I2 GENERAL BIOLOGY 



or under a pocket lens; carefully lift off the roof of the 

 abdomen, (already loosened at the sides by the trim-off of 

 the margins,) by seizing it in front with the forceps. 



This will expose the gill chamber, which occupies the 

 greater part of the abdominal cavity, and terminates the 

 alimentary canal. The severed posterior end of the stomach 

 will be seen in the middle in front, terminated in the rear by 

 a dense cluster of nephridia (Malpighian tubules) and 

 followed by a slender, white, ventrally curved and much 

 concealed intestine, joining it to the gill chamber. On 

 either side of the stomach will be seen a large, silvery white 

 air trunk, which breaks up posteriorly into a great brush of 

 lesser branches that penetrate the walls of the gill chamber. 

 This chamber itself, will be somewhat collapsed ; it may be 

 distended by injecting air or water through the anal aper- 

 ture with a fine-pointed pipette; its longitudinal extent 

 may be seen by lifting the stomach with a forceps and 

 drawing it forward. If turned to one side, a ventral 

 longitudinal tracheal trunk may be seen on either side of 

 the body, breaking up in the rear, like the dorsal trunk, 

 into a multitude of branches, and entering the walls of the 

 gill chamber from below. 



Through the transparent walls of the gill chamber may 

 be seen lines of the black pigment that occupies the 

 bases of the internal gill plates. Discovering thus the 

 location of the rows of gills, the chamber may be safely 

 opened by inserting the point of a fine scissors and cutting 

 the wall for its entire length between two rows. The 

 circular muscles of the wall will, by their contraction turn 

 the whole organ inside out, and fully expose the rows of 

 beautiful, feathery, purplish tinted gill plates. Then if a 

 row be isolated with scissors and mounted on a slide in 

 water, a few individual gills may readily be isolated with 

 needles under a dissecting lens, covered, and studied with 



