The Development of Ischnochiton. 573 



with equal force in the case of Katharina. In some places in the 

 vicinity of Monterey Bay the rocks are literally covered with the 

 adults, and the number of eggs laid by every female must be fully 

 twice ^) the average number of eggs laid by Ischnochiton^ yet the 

 following winter or spring shows a surprisingly small number of young 

 specimens. 



The development proceeds with considerable rapidity. Twenty- 

 four hours after the eggs are laid the larvae commence to rotate 

 within the egg membranes; six days later they break through the 

 chorion and swim about freely for a period lasting from fifteen minutes 

 to two hours. After this time they settle on the rocks and seaweeds 

 and undergoing a slight metamorphosis during the next ten or twelve 

 days they assume the external characters of the adult. 



3. Methods. 

 Several methods of killing and fixing have been tried, by which 

 the albumen in which the eggs are imbedded would not shrink when 

 brought int(f alcohol. With the usual methods this shrinkage occurs, 

 and the eggs become so contorted that the material is almost useless. 

 Flemming's fluid gave excellent results. Specimens were killed and 

 fixed for about six hours, and were then washed in water for about 

 two hours more. By this time the albumen ceases to be viscid, and 

 assumes a consistency like that of coagulated white of egg. The 

 chorion has delicate forked processes projecting from it (Fig. A) to 

 which the albumen strongly adheres , and upon stretching this latter 

 with needles, the projections remaining fixed, the chorion splits at 

 right angles to the tension and the egg drops out. By simply split- 

 ting the string longitudinally with a fine needle hundreds of eggs per 

 minute may be freed from their membranes. They are then washed 

 for another hour in water, run through the different grades of alcohol, 

 and permanently preserved in 90 ^/o alcohol. Eggs killed in this way 

 afford in direct sunlight wonderfully fine surface views. They are 

 perfectly opaque, black as ebony, resting nuclei are fairly clear, and 

 mitotic figures are often indicated, and owing to the full round out- 

 lines of the cells their boundaries come out with the greatest dis- 

 tinctness, rendering the relations of the cells in general of comparatively 



1) I have made an approximate estimate of the number of ripe 

 eggs in the ovary of Katharina., and I believe the above assertion is 

 not far from correct. 



