SUMMARY OE CURRENT RESEARCHES. 
377 
well-developed optic vesicles, originating as outgrowths of the thala- 
mencephalon, and uniting together in the middle line (as shown by 
Locy). 
(2) In Teleosts and Amia there is also a pair of epiphysial outgrowths 
arising in a similar way (with more or less displacement), but the right 
vesicle alone gives rise to the epiphysis, the left one degenerating 
(Hill). 
(3) In Cyclostomes there is also a pair of epiphysial outgrowths, 
which suffer displacement so that the right vesicle comes to overlie the 
left. The right forms the parietal eye, the left one the “ parapineal 
organ.” These two, together with the nerve of the parietal eye, con- 
stitute the “ epiphysis ” (compare Alilborn, Beard, Gaskell, Studnicka). 
(4) In SpJienodon and Lacertilia the epiphysis is a composite struc- 
ture in which the paraphysis and “ Zirbelpolster ” take a very large share, 
while the parts which correspond to the paired epiphysial outgrowths 
of fishes take a very small one. These outgrowths originate, however, 
very much as in fishes, and are subject to more or less displacement, 
and one or other of them may give rise to a parietal eye. In SpJienodon 
it is the left parietal eye which is thus developed. 
(5) The right parietal eye is represented in SpJienodon by the “ pari- 
etal stalk.” In Lacertilia the parietal stalk represents either the right 
or the left parietal eye. 
(6) The parietal eye has no real connection with the parietal stalk 
beyond that of fellowship, and is supplied with a special nerve of its 
own derived from the parietal stalk. 
(7) The ancestors of existing vertebrates possessed a pair of parietal 
eyes, which may have been serially homologous with the ordinary verte- 
brate eyes. 
Influence of Freezing on Hen’s Eggs.* — M. Etienne Rabaud reports 
on certain experiments which he began along with the late M. Camille 
Dareste. The eggs were placed for half an hour in a mixture of salt 
and ice, at a temperature of - 18°, and then variously treated. 
(1) Some were placed immediately in an incubator at 38°, and left 
for three days. It was then found that most of them had developed. 
A third of the number showed living embryos much deformed, or dead 
embryos with a primitive streak and the beginning of the medullary 
groove. The others showed blastoderms much extended over the yolk, 
but without any trace of embryonic differentiation. A few normal forms 
occurred. 
(2) Another set was warmed gradually, but this made no appreciable 
difference in the results. 
(3) In a third set the frozen eggs were not warmed until three days 
after removal from the freezing mixture, but this made little difference. 
The majority in all cases showed a blastoderm without an embryo. 
The results show that a temperature of - 15° is not fatal, but a lasting 
and profound perturbation results, viz. proliferation without differentia- 
tion. There is, however, evidence of individuality, for some formed 
abnormal embryos, and a few were normal. Rabaud is led to the 
^suggestion that different kinds of plasm in the egg react differently. 
* Comptes Rendus, cxxviii. (1899) pp. 11S3-5. 
