354 



HISTOLOGY 



FIG. 318. Nephrostome of the earthworm Lum- 

 bricus herculeus. cf. , centrifugal cell ; c.c.,cen- 



granular texture and a lemon color. They receive the name of chlo- 



r ago gen cells. This substance in- 

 creases in bulk until the cytoplasm 

 is for the most part filled by it, 

 and the nucleus is crowded to 

 the margin of the cell (Fig. 320, 

 A, B, and C). Such cells fre- 

 quently, if not always, when 

 found in the epithelium, lie over 

 a small capillary or space as in- 

 dicated in Figure 320, A, nv.c. 

 These cells leave the epithelium 

 to become wandering cells or 

 amoebocytes. Figure 320, C, 

 shows three such cells that had 

 left the epithelium and were 

 found lying in the ccelom cling- 

 ing to each other as indicated in 

 the figure. 



In Unio the epithelium of the 



tral cell ; cp., centripetal cells or marginal cells, pericardial COBlom in the region 

 (After BENHAM.) r r . . ' ? 



of each auricle, is thrown into 



folds to form a gland known as the pericardial gland. The tissues of 

 this gland are in inti- 

 mate contact with the 

 walls of the heart, pene- 

 trating the tissues of 

 the heart. By these 

 pericardial glands, nu- 

 merous wandering cells 

 or amcebocytes are 

 formed. 



These amcebocytes 

 when they begin their 

 activity are spherical to 

 oval in shape. Their cy- 

 toplasm is rather dense 

 and may contain one 

 or more vacuoles. They 

 are rather small at this 

 stage, measuring about 

 ten or twelve microns in diameter. The nucleus in the early stages of ex- 

 cretion activity is oval, with a diameter of about five or six microns. It 



ex. c. 



FIG. 319. Transverse section through the kidney of Ammo- 

 cotes. One central glomus may be seen, covered with 

 excretory cells (ex.c.); cil.t., ciliated part of tubule. (After 

 HALLER.) 



