2l6 ELEMENTARY EIOLOGV. [CIIAP. 



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 h. Their 7iuclei; 

 rounded or oval, each frequently surrounded by 

 a clear refractive halo. 



^. Fervicjit cells ; each containing a single large 

 secretory globule, which does not decompose the 

 Osmic Acid. Their iiuclci ; 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. 



./. 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. 



Y. 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._/^). 

 It consists of — 



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

 sition as above. 



b. The muscular segment ; a distensible sac, overlying 



