584 Recent Literature. ` [August, 
growth of the “tentacles” (?) in Aurelia to form the “mouth 
opening,” and the statement of the position of the eyes. The 
obscurity comes from the use of the word fringed as applied to 
the edges of the “mouth opening” and the margin of the disk. 
The sense organs of Aurelia have no connection with the walls 
of the “ mouth opening.” I find no authority for the statement 
that the “ square mouth opening ” in Aurelia flavidula is formed 
by the union of four “tentacles.” I have also studied the 
live ephyra of Cyanea and Aurelia, and find no such method of 
formation of the mouth in these genera. 
It is to be regretted that the splendid memoirs of Eimer and the 
Hertwigs could not have been quoted at greater length. Much, of 
course, had to be omitted to prevent the book assuming undue 
proportions The discovery by the latter that the otolith of the 
Trachynemidz is endodermic, while that of the free medusa of 
the Campanularians is ectodermic, is one of their most important 
discoveries, and should be mentioned. 
The statement on page 62 by which the “ Discophora” are 
made to differ from the Hydromeduse “ in developing directly 
from eggs,” and that on page 68 that Pelagia (“ campanella” ?) 
cyanella does not undergo a metamorphosis but “ grows directly 
from the eggs” would leave one unfamiliar with the embryology 
of these animals in doubt as to what is meant by a direct develop- 
ment from the egg. Pelagia differs from Aurelia in that it never 
passes through an attached strobila stage. : 
In view of the elasticity of the word homology in recent times, 
_one is not surprised to find the foot of a mollusk compared to the 
under lip of a worm (?), or vice versa (p. 12). It is doubtful 
whether such a comparison would be accepted by all naturalists, 
and questionable whether it should be introduced as an illustra- 
tion of the term in a text book. The term homology, like many 
others (polymorphism, individual, &c.) is yet to be accurately 
defined in a manner acceptable to all. At present there 1s no 
better illustration of the term than the old comparison of the 
wing of the bird and the arm of man. —¥. W. F. 
STUDIES FROM THE MORPHOLOGICAL LABORATORY IN THE UNIVER- 
SITY OF CamBripGe.'—This thick. brochure is mostly taken up 
ith embryological papers which have appeared during the past ygar 
in the Quarterly Journal of Microscopical Science and the Proceeg- 
ings of the Cambridge Philosophical Society. The papers relate 
mostly to the special points in the development of the Vertebrates. 
The first paper relates to the existence of a head-kidney in the em- 
bryo chick together with some points in the development of the Mül- 
lerian duct. In this paper Messrs. Balfour and Sedgwick record the 
existence of certain structures in the embryo chick, which event 
1 Edited by F, M. Balfour, M.A., F. R. S., Williams and Norgate, 1880. 8° pP- 
Tog. 10 pl 
