SALTER ON THE EERTILITY OF HYBRIDS. 
279 
The one striking point of these experiments (which, I believe, has 
never been noticed before) is that a large proportion of these eggs 
from hybrid birds, breeding inter se, have failed to produce young, 
not from absolute sterility, but from sterility in degree—from an 
amount of vitalization insufficient to carry out the whole result of 
reproduction; or, where the young individual has been completed, 
leaving it with vital resistance too feeble to maintain life and cope 
with common and customary external influences. 
These phenomena have a singular parallel in the circumstances 
attending parthenogenesis, when it occurs exceptionally in certain 
Articulata that do not normally reproduce their kind in this manner. 
In a note published by Mr. Lubbock, in the 7th number of the 
Natural History Beview, p. 345, an epitome is given of some re¬ 
searches conducted by M. Jourdan respecting non-sexual generation 
in the Silk-worm moth; and it appears that, though some few of the 
unimpregnated eggs from this insect produced young larvse, many 
others underwent the early stages of embryonic development and 
then stopped. And further, Mr. Lubbock informs me that in some 
other cases where virgin-reproduction is exceptional, the young thus 
produced are stated to have perished without obvious cause. 
Whether any of these young are, under these circumstances, de¬ 
formed, is a point upon which, I believe, there is no evidence. It 
seems clear, however, that both in the hybrid-breeding of birds and in 
exceptional parthenogenesis there is the same kind of defect; that 
the sterility is not absolute but in degree ; and that the stimulus, 
whatever it may be, which starts the embryonic changes is feeble and 
imperfect rather than wholly wanting. 
XXVI.— On the Brain of the Siamano. (Hylobates syndactylus , 
Baffles.) By William Henry Blower, Conservator of the Museum 
of the Boyal College of Surgeons. 
It has been observed by Professor Huxley that, “ if the Primates 
“ were arranged according to the development of their posterior 
“ cerebral lobes, we should have some such descending series as 
“ the following :— Chrysothrix , Cebus , Troglodytes , Man, .... 
“ Mycetes —a series which sufficiently illustrates the classificatory 
“ value of these structures.”* The extended observations which have 
been recently made on the subject have afforded a more complete 
elucidation of this remark. The various genera hitherto examined 
may, I think, be placed approximatively in the following order *.—an 
* On the Brain of Aidespaniscus. Proc. Zool. Soc. June 11th, 1861. 
