EXPLANATION OF THE PLATES. XV 11 



Fig. 16. Three cells from the kidney of Helix aspersa. The contained 

 secretion is dead white, and presents a chalky appearance. 



Fig. 1 7. Two cells from the vesicles of the testicle of Squalus cornubicus. 

 The contained bundles of spermatozoa are developed from 

 the nucleus each spermatozoon being a spiral cell. 



PLATE V. page 412. 



Fig. 1. Five cells from the mamma of the bitch. In addition to their 

 nuclei, these cells contain milk-globules. 



Fig. 2. A portion of duct from the testicle of Squalus cornubicus. A 

 few nucleated cells, the primary or germinal cells of the 

 future acini, are attached to its walls. 



Fig. 3. The primary cell of an acinus in a more advanced stage. The 

 nucleus has produced a mass of young cells. The pedicle 

 appears to have been formed by the germinal cell carrying 

 forward the wall of the duct. A diaphragm accordingly 

 presents itself across the neck of the pedicle. 



Fig. 4. A primary cell in a more advanced stage. 



Fig. 5. A primary cell still more advanced. 



Fig. 6. Some of the secondary cells, products of the nucleus of the 

 primary cell, are cylindrical, and are arranged in a spiral. 



Fig. 7. The change into cylinders, and the spiral arrangement com- 

 pleted. 



Fig. 8. a. One of the secondary cells ; its nucleus a mass of young cells. 

 6. A secondary cell elongated into a cylinder, each cell of its 

 composite nucleus elongated into a spiral, c. The spiral cells 

 or spermatozoa, free. 



Fig. 9. A bunch of acini, in various states of development, maturity, 



and atrophy. 



The four following figures are diagrams, arranged so as to illus- 

 trate the intimate nature of the changes which occur in vesi- 

 cular glands when in a state of functional activity. 



Fig. 10. A portion of gland-duct with two acini. One of the acini is 

 a simple primary cell ; the other is in a state of develop- 

 ment, its nucleus producing young cells. 



Fig. 11. Both acini are advancing; the second has almost reached 

 maturity. 



Fig. 12 The second acinus is ready to pour out its contents, the first 

 to take its place. , 



Fig. 1 3. The second acinus is in a state of atrophy, the first is ripe. 



Fig. 14. Two follicles from the liver of Carcinus mcenas. The colour- 

 less germinal spot is at the blind extremity of the follicle. 

 The secreting cells become distended with bile and oil as 

 they recede from the germinal spot. 



