36 



THE OLEAGINOUS AND ALBUMINOUS 



dinary extent, a species of organization in the yolk, such as is 

 observable in no other class of animals. This is as conveniently 



(fig. 1 9) it may be seen that there are three separate organs necessary to the 

 formation of the egg, namely, the yolk-bearing (vitelligenous) organ (ft), which 



generates the oleaginous substance ; the albumen- 

 bearing (germigenous or germ-forming) organ (oc)i m 

 which the albumen originates and develops into ger- 

 I minal vesicles; and the womb (uterus) (w^),into which 

 the germinal vesicles descend and where they are each 

 separately enveloped in a portion of the yolk, which 

 pours into the uterus in certain quantities as it is 

 needed, and there forms, with the germinal vesicle, a 

 perfect egg (w). The uterus then forms a shell about 

 the egg, and it is ready to be laid. In other worms, for 

 instance, the Round-worm (Ascaris), the formation of 

 the yolk and that of the albumen are carried on in 

 comparative proximity to each other, but yet in dif- 

 ferent parts of the same organ, and after a while the 

 germinal vesicles (albumen) pass into the yolk (oil) 

 bearing part of the organ, and are there enveloped 

 separately with a quantity of yolk, and the egg is 

 completed. This same process is known to take place 

 in certain Insects; for instance, the common cricket 

 (Acheta), &c. Again, in Spiders, the diversity of 

 local origin is still less than in the last ; the germinal 

 vesicle is developed, in a saccular body, to a certain 

 extent, and then the yolk grows about it. Finally, 

 we may find, as in the clams (Venus), &c., the ger- 

 minal vesicles scattered through a mass of yolk, which 

 in process of time is broken up into groups or con- 

 cretions, each one of which becomes connected with a germinal vesicle, and 

 surrounded by an envelope which forms a kind of vitelline sac. 



Fig. 19. Prostomum lineare. CEst. Natural size about 1-1^'" (line) long. 

 View of the lower side. 0, mouth ; ph, the first part, and ph*, the second part 

 of the throat ; w, v l , the stomach ; n 1 , the central part of the nervous system, 

 consisting of a large ganglion on each side of the throat, joined by an inferior 

 commissure, n ; m 1 , the sucking disc, a sort of prehensile apparatus ; /, us, pe, ga, 

 the male portions of this double organization ; the female reproductive organs 

 are, vi, the yolk-bearing organ, ov, the germ-forming organ, and ut, the womb, 

 at present occupied by a single egg, w ; rs, accessory fertilizing receptacle ; R, 

 R, the exterior openings of the water canals, r, r, r 1 , r 1 , r 2 , r z . From Schultze. 



Ffc. 19. 



