264 C. O. WHITMAN. 



this, in so far as it is the architect of its own destiny. Tlie 

 raw material is first split into two, four, or more huge masses, 

 and some or all of these into secondary masses, and some 

 or all of these into tertiary masses, &c., and out of these 

 more or less unlike fragments the embryonal building-stones are 

 cut, and transported to their places of destination. The cleavage 

 in Clepsine has been described by Grube, Rathke, and Robin, all 

 of whom have fallen into some grave errors, in consequence of 

 which the cardinal points of the process were missed. On this 

 head I can speak with the fullest assurance, for I have followed 

 the cleavage in four species, and have seen it many times over in 

 two of those species. What I have seen in living eggs is veri- 

 fied in the most positive manner by my sections. 



a. First two Meridional Divisions (PI. XII, figs. 12-19). — 

 At the approach of the first division, as we have before remarked, 

 the egg has a long elliptical form, flattened at the poles. The 

 aboral ring-disc is reduced to a mere point, slightly stellate, and 

 the oral disc has assumed the form of a crescent, the two horns 

 of which point towards the plane of the advancing division. 



The egg takes an oblong, slightly biscuit-sliaped form as the 

 cleavage depression passes (figs. 13 and 14, 3 h.) gradually from 

 the upper to the lower pole. In rare cases this cleavage encircles 

 the entire egg from the moment of its apjjearance. By the time 

 the groove has passed about one third of the distance towards 

 the centre of the egg; the plane of division takes the form of a 

 fine line, owing to the fact that the two segments are checked in 

 their movement away from each other by the egg-membrane, 

 rig. 15 (3 h. 30 min.) represents the egg after the completion of 

 the division. It will be observed that the walls of the groove 

 approach each other sooner at the upper than at the lower pole. 

 A few minutes later the two segments appear to be separated 

 only by a fine but well-defined line, and 30 minutes later 

 (4 h.) the egg presents the oval form of fig. 16. The remnant 

 of the oral ring-disc, seen on the larger segment, has a clouded 

 appearance, and is without the slightest indications of rays. 

 A trace of the aboral disc is sometimes still visible, but in 

 most cases no longer recognisable. Thirty minutes later the 

 remnant of the upper disc is considerably smaller and less 

 distinct, while the white border, which has encircled the ring 

 substance from the beginning, has grown larger, reaching over 

 to the corresponding pole of the smaller segment. At this time 

 the whole oral pole seems mantled with a greyish-white sub- 

 stance, the character of which has before been indicated. The 

 second division begins from 60 to 90 (5 h.) minutes after the 

 completion of the first (fig. 17). As this division begins the. 



