ON THE CLEAVAGE OF AMPHIBIAN OVA. 
E. O. JORDAN anp A. C. EYCLESHYMER. 
Our observations upon the early cleavage stages of several 
sorts of amphibian eggs were made primarily with a view to 
determining the extent and frequency of cleavage variation. 
The eggs examined were those of two species of Urodela, — 
Amblystoma punctatum and Diemyctylus viridescens — and two 
Anura, — Rana palustris and Lufo variabilis. 
The unsegmented eggs of Amdblystoma were usually collected 
before eight o’clock in the morning, and began to segment at 
three or four o’clock on the afternoon of the same day. As 
we hope to show presently, there is reason to believe that there 
is an interval of nearly ten hours between the laying of the eggs 
and the appearance of the first furrow ; these eggs, therefore, 
were probably laid at about five or six o’clock in the morning. 
Other bunches of Amdblystoma eggs were in the early stages of 
cleavage when collected in the morning, and these were 
undoubtedly deposited on the preceding evening. Clarke (80) 
states that most of the eggs laid by the Amdblystoma in his 
aquaria “were laid during the night, and by nine o'clock the 
next morning the first segmentation furrow had usually made 
its appearance.” 
The eggs of Dezemyctylus are best ‘obtained from females in 
captivity, and can be removed from the membrane as soon as 
laid (Jordan, '93, p. 275 ef seg.). The first cleavage furrow 
appears about ten hours after laying. Since there is a close 
correspondence in all other time phenomena between the egg 
of the newt and the egg of Amblystoma, we are justified in 
1 Born (Anat. Anz. VII, 1892, p. 809) refers to a paper by Grénroos, which we 
have, unfortunately, been unable to see (Ueber die Eifurchung bei den Tritonen. 
Diss. inaug. Helsingfors, 1890). According to Born, Grénroos has shown “ dass 
bei gewohnlicher Zimmertemperatur die erste Furche an reifen Tritoneiern 5-6 
Stunden nach der Besamung auftritt— gemeint sind natiirlich Uteruseier —im 
Gegensatz zu den Eiern unserer einheimischen Anuran bei denen unter gleichen 
Bedingungen der Eintritt der ersten Furche nach 3 Stunden erfolgt.” 
