498 CLAPP. [Vol. V. 



Relation of the Axis of the Embryo to the First 

 Cleavage Planes. 



The question of the coincidence of the first or second plane 

 of cleavage with the axis of the embryo is one that has attracted 

 considerable interest of late. As the egg of Batrachus offers 

 unusually favorable conditions for deciding this question, I have 

 undertaken some experiments expressly for this purpose. 



It is well known that the eggs of Batrachus are adhesive. 

 They may be found attached to the under side of boards or 

 stones, or to the inside of tin cans, in the shallow water of the 

 bays or inlets along the coast. A cavity is often excavated 

 beneath a large stone by the parent fish, and the eggs deposited 

 on the roof of this cavity. 



The adhesive disk, as represented in Fig. I. /, is about 3 mm. 

 in diameter. It is a transparent thickening on one pole of the 

 egg membrane, at the time of oviposition, and by means of it 

 the egg is glued firmly to the rock. 



The blastoderm develops at the free pole of the egg, as seen 

 in Fig. I. a and b, so that the first stages of cleavage can easily 

 be seen with a lens through the egg membrane. 



On the 22d of June eggs were artificially fertilized. 



Having chloroformed the fish, the abdomen of the female was 

 opened, and the ovaries cut so as to allow the mature eggs to 

 fall and fasten themselves to the bottom of shallow glass dishes. 

 The testes of the male were removed, and after being cut "into 

 fragments, were placed in the dishes with the eggs. Soon after 

 this the eggs were supplied with fresh sea-water and left to 

 develop. The adhesion of the yolk to the egg membrane, as it 

 rested on the disk area, prevented rotation. 



The first line of cleavage appeared seven hours after fertiliza- 

 tion, and on the seventh day the axis of the embryo could be 

 distinctly seen as a light streak in the' blastoderm. 



The method of determining the relation of the first cleavage 

 planes to the axis of the embryo was as follows : — 



The exact position of each egg was represented by circles on 

 paper, and the paper and the dish containing the eggs were 

 oriented by fastening a label on each in the same relative posi- 

 tion. When the first line of cleavage appeared, the direction 

 was indicated in the circle representing that egg, by the diam- 



