2l6 ELEMENTARY BIOLOGY. [CHAP. 



to a glass slide bearing a drop of Osmic Acid solu- 

 tion; wash, when sufficiently stained, and examine 

 under a high power. 



Note that the cells are arranged in aggregates 

 and flattened, as the result of mutual compression. 

 Look for 

 a. Hepatic cells ; characterized by the presence of 



fatty globules, differentiated as at b. Their nuclei; 



rounded or oval, each frequently surrounded by 



a clear refractive halo. 



/?. Ferment cells ; each containing a single large 

 secretory globule, which does not decompose the 

 Osmic Acid. Their nuclei ; larger than those of 

 a and oval, they usually contain a single nu- 

 cleolus. 



The larger of these cells (the older of the series) 

 will be found in or near the middle of each group. 



d. Compare similar sections of material, hardened in 

 alcohol and stained with borax-carmine. The nuclei 

 of the hepatic cells stain with great intensity. Look 

 for stages in the elaboration and discharge of the 

 secretory product of the ferment cell. 



F. The excretory-organ or green gland. 



i . Dissect from the left-side, and remove the greater part 

 of the exposed cephalic shield. The entire organ lies 

 in the extreme front part of the cephalo-thoracic 

 cavity, Immediately in front of the gullet (cf. Sect. D._/i). 

 It consists of 



a. The glandular segment ; a soft greenish mass, po- 

 sition as above. 



b. The muscular segment ; a distensible sac, overlying 



