16 DEVELOPMENT OF THE PROG'S EGG [Ch. II 



place of a large watery nucleus only a small mass of chromatic 

 substance, lying in the protoplasm, is present. An achromatic 

 spindle appears, and the chromatin in the form of granules is 

 arranged at the equator of the spindle. The spindle lies at the 

 surface of the egg near the centre of the black hemisphere 

 (Fig. 11, A). It lies also in the centre of the fovea, which is 

 found on the surface of the egg. The fovea marks the former 

 position of the large ovarian nucleus, and although the nuclear 

 membrane of the original nucleus has disappeared, and its 

 watery cavity has been encroached upon by the surrounding 

 protoplasm, yet the pigment has not penetrated very deeply 

 into this region. The eggs pass in this condition from the 

 body-cavity into the oviducts. Newport ('51) believed that, 

 owing to the close attachment of the oviducts at their inner 

 openings to the walls of the pericardium, at each contraction of 

 the heart the slit-like openings of the oviducts would gape open, 

 and any eggs in the vicinity might be forced into the mouths 

 of the tubes. Also, he thought that owing to the muscu- 

 lar movements of the body, and the resulting shifting of the 

 internal organs, the eggs sooner or later pass near the openings 

 of the oviduct, and are then carried into the tube. At any 

 rate, there seems to be not much ground for the older state- 

 ment that the mouths of the oviducts actually grasp the eggs 

 by a muscular movement like that of swallowing. According 

 to Nussbaum ('95), the eggs, when set free from the ovary into 

 the body-cavity of the frog, are carried into the open mouths 

 of the oviducts by the motion of the cilia of the coelomic epi- 

 thelium. These cilia drive anteriorly any bodies lying free 

 in the body-cavity. If, for instance, eggs taken from one frog 

 be placed in the vicinity of the openings of the oviducts in 

 the body-cavity of another frog, they will be carried into the 

 open mouths of the oviducts by the action of the cilia in that 

 region. 



The cilia do not cover the entire surface of the coelomic 

 epithelium, and there are certain recesses in the body-cavity 

 destitute of cilia. The eggs that accumulate in these recesses 

 will be sooner or later forced out into the general cavity as a 

 result of the alternate contractions and expansions of the ven- 

 tral musculature of the body-wall, as well as by the changes 



