480 REPORT—1896. 
number of pelagic ova which I have been able to examine, there is a 
distinct, though very much modified, vitelline circulation. The elements 
of this circulation are not, however, blood corpuscles, but yolk corpuscles. 
In the ova of etght species! I found this circulation, the corpuscles of 
which are derived from the periblast. Contemporaneously with the 
formation of the heart have appeared the primary vessels—viz. (a) the 
two lateral arteries uniting to form the median trunk, which passes 
posteriorly a point a little short of the tip of the tail ; (b) the primitive 
caudal vein, which debouches into the posterior end of the yolk-sac. The 
pulsations of the heart are at first feeble and slow. The venous end of 
the heart is open to the interior of the yolk-sac. A few corpuscles are 
now seen to pass from the yolk-sac into the heart. These corpuscles, 
which proceed singly and at intervals, are seen moving along the arterial 
trunks to the tail, and immediately thereafter appear in the caudal vein, 
from which they pass into the yolk-sac. They then, with varying speed, 
pass over the ventral surface of the yolk and enter the heart. Some of 
the corpuscles proceed directly from the posterior end of the yolk-sac to 
the heart without ; others become attached to the periblast, and remain 
fast for longer or shorter intervals. On the posterior surface of the yolk, 
where the caudal vein enters the yolk-sac, the periblast shows a well- 
marked furrow, which has been worn in it by the circulating fluid. 
Before the heart begins to beat, corpuscles, similar to the later 
circulating corpuscles, are seen on the periblast, and that these cor- 
puscles, derived from the periblast, become the circulating corpuscles 
there is no doubt. At first, and even up to the time of hatching, the 
corpuscles are few in number. Only in the case of the three species of 
the eggs of Murenide have I been able to study the circulation fully. 
Eggs of other species which I examined presented difficulties, owing to 
their small size, presence of oil globules, or on account of the supply of 
specimens being insufficient. Only in the case of two species, in addition 
to those of the Murznide, was I able to obtain the ova in abundance. 
The corpuscles are minute, irregular in shape and size. In certain of the 
eggs the presence of the corpuscles on the periblast, and in motion in the 
yolk-sac, the connection between the caudal vein and yolk-sac, and the 
furrow continuing the caudal vein on the periblast have been regarded as 
sufficient evidence that a circulation of yolk corpuscles, similar to that 
clearly followed in others, was present. A certain amount of yolk- 
absorption no doubt takes place at the parts of the embryo in connection 
with the yolk, but after the formation of the tail of the embryo that 
absorption is probably very slight. The heart of the embryo in a pelagic 
ovum is said to pulsate before any blood is present, but the heart is not, 
however, without a circulation. It is extremely probable that there is, in 
addition to the yolk corpuscles, a circulating fluid of some sort being 
directed through the vessels by the heart. The first corpuscles are then 
formed in the periblast, and pass into the circulating fluid, the existence 
of which it is not unreasonable to postulate. A second method of adding 
corpuscles to the circulation is shown in a number of ova. This is a 
process of budding from the periblast. Slender pseudopodium-like pro- 
1 The eight species included:—Ova of Murenide, Raff. (three species) ; 
Pleuronectes italicus (?); Merluccius vulgaris; Engraulis encrasicholus; Species 
No. 3 (Coryphena ?), Raff.; Uranoscopus scaber. (In the case of the last species I 
refer to a stage previous to the appearance of the complete vitelline circulation.) 
