408 JORDAN AND EYCLESHYMER. [Vor xe 
concluding, as we have already intimated, that in this respect 
also, there is time agreement, and that the eggs of Amblystoma, 
as well as those of the newt, begin to segment about ten hours 
after they are laid. 
The eggs of Rana and Bufo may be found unsegmented in 
the ponds in the early morning. The first furrow appears, as a 
rule, earlier in the day than it does in Ammdlystoma. We did 
not particularly question this point, however, since Newport 
(Phil. Trans. 1851, 1853, 1854) long ago determined that the 
frog’s egg begins to segment in from four to five hours after 
the spermatozoa are applied. Our own incidental observations 
upon the eggs of the frog and toad amply confirm this result. 
All the eggs when brought to the laboratory were put under 
uniform conditions — in shallow dishes of water at about 18° C. 
The cleavage stages were followed in the living egg with the 
aid of the Zeiss dissecting microscope. A plane mirror placed 
underneath the flat and thin-walled glass dish in which the egg 
rested enabled us to observe accurately the progress and posi- 
tion of the furrows in the lower hemisphere. 
The exact time of appearance of each set of furrows was 
noted in all cases, and is recorded on most of our figures. 
The following table expresses this record in a condensed form, 
the times given for the inter-cleavage periods representing the 
average of our observations on some fifteen to twenty eggs in 
each stage.? 
Amblystoma. Rana. Diemyctylus. Bufo. 
Interval between fertilization and rst cleavage.| ro hrs. (?) 4-5 hrs. ro hrs. 4-5 hrs. 
Interval between 1st and 2d cleavages . thr. 50m. |1 hr. 15m. | 2 hrs. 1 hr. 5 m. 
Interval between 2d and 3d cleavages thr: 5s.m.. | 2 hr. 15m. |\-w hr. 45m. | cbr: 
Interval between 3d and 4th cleavages . 2 hrs. 1 hr. thr. 40m. | rhr. 
Interval between 4th and sthcleavages . 1 hr. 40m. thr. 50m. | 1 hr. 
Interval between 5th and 6th cleavages . .| [cr hr. 35 m.] [2 hrs. 45 m.] 
Interval between 6th and 7thcleavages . $) ie hr.-25¢m.] (2 hrs. 45 m.] 
Interval between 7th and 8th cleavages . .| (r hr. 25 m.] 
Interval between 8th and oth cleavages . .|| {x hr. 25 m.] 
Interval between oth and i1oth cleavages .| [x hr. 30 m.] 
1 The times enclosed in brackets refer to individual cases, and are not averages. 
The Amélystoma egg, in the instance recorded, happened to have a quicker rhythm 
than the majority, and the Diemyctylus egg a slower rhythm. 
