IN DAFHNIA, AND OF THE STEUCTUEE OF THE EPHIPPIHM. 
91 
In warm summer weather, about fom: days after the deposition of the preceding brood 
of eggs, those whose development we have thus briefly traced are ready to make their 
entry into the receptacle ; the last brood having in the meantime acquired the power of 
motion, and become fit to sAvim about freely in the water. Very shortly after the exclu- 
sion of the young, the Dajplinia sheds its skin, and again soon after that the eggs are laid. 
In what manner this takes place I am unable to say ; and that a duct large enough for 
the passage of the eggs, which, when laid, measure about o? should be often quite 
imperceptible, should certainly teach us much caution in describing the anatomy of the 
lower animals. According to Strauss, the eggs pass from the posterior part of the ovary 
into the receptacle, but in the only specimen in which I observed the process, they 
appeared to emerge close behind the heart. 
Sevei-al times it happened that at the time of laying, some of the egg-matter remained 
in the ovary. This was not deposited soon after, as might have been expected, but in 
one case gindually disappeared; in several it was hidden by the succeeding brood of eggs, 
and in one it became more diffused, and the creature died. 
I have always found these eggs, when crushed shortly after deposition, to consist chiefly 
of globules of various sizes, which do not appear to possess any distinct membranes, as 
they gradually run together into large masses. Moreover, if they are placed between 
two pieces of glass, and after the egg has bm’st, the upper bit of glass is rolled backwards 
and forwards upon the lower, the globules run together and form small homogeneous 
cylinders. If a somewhat older egg is examined, there will be found also a number of 
minute chcular cells, about *0005 of an inch in diameter, and forming a sort of membrane. 
These, I beheve, constitute the blastodermic layer. 
I know not whether the contact of living membrane is necessary for the development 
of these eggs, but certainly none survived of those which I removed from the receptacle 
for the pmqjose of watching. 
In many cases the eggs contained a large and distinct globule*, but this is, I believe, 
merely a large oil-globule; and when the egg is crushed, it appears to have no cell-wall. 
I have found it much larger and more distinct in the eggs of D. pulex than in those of 
1). Schoefferi: in the latter species, indeed, it was not uncommon in the spring, but 
throughout the summer and autumn, though it was then very conspicuous in B. pulex, 
yet in I). Schcefferi the oil-matter was usually in many small globules. That this is in 
reality a globule, and not a pecuhar cell, was proved by pressure often causing it to 
elongate, and then separate into two smaller balls. 
These large oil-globules arise in the ovary, and may be seen there at an early period in 
the development of the eggs. They appear to be analogous to the “ Nahrungsdotter,” or 
nourishment-yolk, described by J. V. Carus in spider’s eggsf. 
In the Daphnia eggs they remain unchanged until the young is hatched, and is nearly 
ready to quit the receptacle, when they break up into other similar but smaller globules. 
* See Baied, 1 . c. pi. 6. fig. 2. 
t Archiv fur "Wissenschaft. Zool. 1850. 
