102 HANDBOOK OF INVERTEBRATE ZOOLOGY. 



of those eggs which do not hatch. In about twenty-four 

 hours more, place them in a larger tumbler, and fill this 

 up with fresh sea-water, and repeat this every day. After 

 five or six days, it will be best to distribute the larvse 

 among several small tumblers of water, by picking up a 

 few with a dipping-tube, and placing them in each tum- 

 bler. As they grow larger, they may be picked out and 

 placed in a watch-crystal every day while the water is 

 changed. 



If specimens can be found in the act of discharging 

 their reproductive elements, there will be no need of dis- 

 section. If a number of specimens are placed for a few 

 hours in a large tub of sea-water, some of them may dis- 

 charge the brown ova and white male fluid from the ori- 

 fices in the reproductive ossicles. As these reproductive 

 elements settle to the bottom, they may be drawn up 



through a long dipping -tube, and 

 ^ mixed as above described. 



II. ]Microscopic examination of the 



semientino^ eofo;. 



Fig. 43. — A newly-laid egg of Arbacia punc- 

 tulata, magnified about two hundred diameters. 

 (From a sketch by H. Gai-man. ) 



a. Eggshell, h. Yolk. c. Germinative vesicle. 



Fig. 43. 



a. The unfertilized ^^g. When this is examined with 

 the microscope, it is seen to be perfectly spherical (Fig. 43), 

 consisting of an opaque, brownish-red yolk (6), sur- 

 rounded by a thick, transparent shell («). When crushed 

 under a cover glass, the yolk will be found to owe its color 

 to minute reddish granules, or food particles, which fill 

 the transparent protoplasm so completely as to color it 

 uniformly. Near the surface of the yolk, notice a round, 



