48 



CHIM/EROID FISHES AND THEIR DEVELOPMENT. 

 FERTILIZATION. 



Fertilization begins, as in sharks, in the uppermost portion of the oviduct and 

 continues throughout the period of the formation of the capsule.* The earliest 

 stage in the writer's material was obtained from a capsule like that shown in plate iii, 

 fig.^'i 3, earlier stages not having been handled successfully. Late stages were secured 



44 



45 



"fi^ 





^^'^ 



^^^'WtW 



1 Jv 



&^'%'i(S^ ,^ 



■'i 



45^ 45B 



46 



46A 



-r 



"^i^ife*^ 



47 



47J 



.«) '^ 



f'Sv- ,<-, ^^j^^"^ 



© 



'^"^^'"^^^^a^ 





Fig. 44.— Detail of late fertilization stage, showing male nucleus in the process of approaching the egg nucleus. A club-shaped centrosome 



surrounded by astral rays appears at (right) side of nuclear membrane. X 475. 

 Fig. 43.— Detail of section similar to the last. A well-marked vacuole (artifact ?) appears at one end o( nucleus. 

 Fig. 43A. — Sperm nucleus with aster from section similar to the preceding. 



Fig 45B. -Sperm nucleus from stage similar to foregoing. The center of aster is to be found in the section below present one. 

 Fig. 46.- Detail of sechon shown in lig. 34. Sperm nucleus has divided amitoticaily. This at first suggests a stage of copulating 



pronuclei. 

 Fig. 46A. — Egg and sperm nuclei in apposition. Rays not conspicuous. 



Fig. 47.— Early prophase of segmentation nucleus. Two asters are present, one of which (the right) contains two centrosomes. 

 Fig. 47A.— Early segmentation stage. Section passing through segmentation nuclei. No surface furrows are as yet present. X 190- 



from capsules about as shown in plate iii, fig. i6. In the present account the 

 stages may conveniently be referred to as early, middle, and late. 



An early stage is shown in surface view in plate iv, fig. i8, magnified about 

 15 diameters. This was drawn from a living egg and shows the germinal area 

 somewhat misshapen, due to rupture of the vitelline membrane, f The germinal 

 area is not sharply outlined ; it is the same color as the remainder of the egg, and 



* The egg at deposition is undergoing the first stage of segmentation, 

 t This is conspicuous at this stage, glossy and tense. 



