THE NAUTILUS. 19 



Haematoxylin and orange G. in ninety-five percent alcohol were 

 used as stains. 



In order to establish the relation of the brood pouch to the 

 ■gill filaments and water spaces a wax model of parts of a gill 

 was constructed from drawings made on an Edinger machine. 



Reproductive Organs. The animal is hermaphroditic. The 

 reproductive organs are situated beneath the pericardium and 

 behind the stomach (Figs 1, 2, 3, 4). They consist of a pair 

 of racemose glands, the anterior part of which produce sperm 

 and the posterior eggs. A common genital duct continues 

 backward, opening into the cloacal chamber of the inner gill 

 near the opening of the kidney. 



Plate V. Fig. 2, represents the essential parts of an egg fol- 

 licle. Each follicle is lined with a single layered epithelium 

 supported by a very heavy basement membrane. Eggs develop 

 by the enlargement of certain cells of the lining epithelium. 

 When a developing egg has grown to four or five times the size 

 of the neighboring cells it is pushed out of its position by a 

 pedestal-like growth of the basement membrane. Thus pro- 

 jected into the lumen of the follicle, it continues to develop until 

 mature, when it drops off. 



The sperm-producing follicles (Fig. 3) are irregularly spher- 

 ical and arranged about their common duct like the parts of a 

 raspberry. Each follicle is made up of a mass of sperm mother 

 •cells about its outer part and either fully formed or young 

 sperm cells near the center. The center is hollow and com- 

 municates with the common sperm duct. This duct (PI. V, 

 Fig. 3) extends a short distance backward where it receives the 

 product of the egg follicle, continuing from that point to the 

 exterior as a common genital duct. 



Regarding maturation and fertilization Stepanof! (1865) ob- 

 serves, "When the egg has reached a certain size it separates 

 more and more from the wall of the basement tissue until it at 

 last becomes free, in the inner part of the follicle and later falls 

 into the outlet of the sex glands. The separation is affected by 

 the increase of the yolk mass and the resulting weight of the 

 egg. Eggs thus fallen into the duct become surrounded by a 

 mass of fully formed sperm, so that, without doubt, fertilization 



