II.] THE CRAYFISH AND LOBSTER. 219 



In the Lobster the ovaries are elongated and pro- 

 longed into the abdomen. Each is a dark green 

 mass, and near their anterior ends the two meet in 

 the middle line and remain confluent for a short 

 distance. An oviduct arises from each ovary a little 

 in front of its middle, and passes directly to the 

 genital opening of its own side. 



3. The genital organs, having been first examined in 

 situ as above directed, may be profitably compared 

 side by side, after removal from the body, together 

 with their related appendages and thoracic sterna. 



A highly instructive view of them may be obtained 

 from the side, dissecting as directed for Sect. I. 3. 



4. Lay open the ovary from the dorsal aspect and wash 

 carefully until quite clean. Examine under water 



a. Its wall ; directly continuous with that of the ovi- 

 duct. 



b. Its central cavity ; similarly continuous with the 

 lumen of the oviduct. 



c. The ovisacs ; spherical masses developed within the 

 wall, they are sometimes irregular in shape owing 

 to mutual compression. 



Examine under a hand-lens. They vary in size, 

 the younger being very minute white bodies irregu- 

 larly scattered in groups throughout the mass ; re- 

 move a few of these, and transfer to a glass slide. 

 Stain with magenta or eosin and examine under a 

 low power, avoiding pressure. 



a. The ovum ; a single large cell, filling the entire 

 ovisac. Note its highly granular vitellus ; its 

 large round germinal vesicle containing a number 

 of germinal spots. 



