182 HUBERT DANA GOODALE 



a day. Hertwig thinks that this type results from polyspermy. 

 It is quite possible that this lot of eggs were made polyspermia by 

 the unfavorable conditions to which they were subjected. 



Later cleavages show many irregularities, which I may not 

 take time to describe since they differ only in minor details from 

 other amphibians, especially those described by Rauber ('83 and 

 '86) and Jordan and Eycleshymer ('94). 



Some observations on the direction and rate of progress of the 

 third set of cleavage furrows. The third set of cleavage furrows, 

 preceded by a deep cavity appearing at the crossing of the first 

 and second furrows, always start from a preexisting furrow as 

 is true also for all other furrows excepting of course the first. 

 They do not first appear on the intermediate points of the blasto- 

 meres. 



In general, when a furrow of the third set is horizontal, the 

 rate of progress for the first fifth of the total distance to be trav- 

 elled is slower than for the second fifth. It then tends to remain 

 constant or to decrease for the next fifth and so on until the fur- 

 row is completed, although there are exceptions to this rule. 



The various furrows may progress either in a clockwise or in 

 a counterclockwise direction. Sometimes they start from both 

 sides of a quadrant and meet at its middle. They may change 

 from a horizontal direction to a diagonal or vertical one, or some- 

 times disappear, perhaps to reappear later. 



DETAILS 



With these general statements in mind wo may take up detailed obser- 

 vations on several eggs. In the accompanying figures, each quadrant 

 is designated by a letter. The cleavage furrows are distinguished by 

 the letters of the adjoining (quadrants, prefixed usually by the numeral 



1 or 2, referring respectively to the first or second cleavage plane. Con- 

 tinuous lines indicate the first appearance of a furrow, dotted lines its 

 next recorded extension, (in fig. 11 dashes were used instead); crosses 

 were used for the next, circles for the next and disks for tlie last. 



Egg no. 28, fig. 10. In quadrant A, the third cleavage began at 6:50 

 as a depression on 1 AD which extended into both quadrants. Eight 

 minutes later the furrow had extended 18°, roughly spcniking, into each 

 quadrant, At tliis time, a minute depression appeared on the vertical 



2 AB. Four minutes later the first furrow had extended another 18°. 



