ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
309 
formed a water-tube, and in that of adult frogs the ciliated epithelium 
may still be seen to drive carmine-granules towards the tail. 
Lepidosteus.* — Mr. E. L. Mark has had the opportunity of studying 
the development of Lepidosteus. He finds that both the egg-membranes 
are radially striated, and he corrects some observations of Balfour and 
Parker. The villi of one membrane are each composed of three parts 
— liead, stalk, and roots ; the last of these project into the pore-canals 
of the zona. The single micropyle of the egg has been overlooked by 
previous observers ; the micropylar apparatus embraces a funnel and a 
canal ; the former results from an infolding and a reduction in thickness 
of both tlie villous layer and the zona radiata. 
The granulosa of the mature ovarian egg consists of a single layer 
of polygonal cells, except in the region of the funnel, where it forms a 
plug of cells that completely fills the funnel. A single large granulosa 
cell forms the apex of the plug, and occupies the bottom of the funnel. 
An egg-membrane comparable structurally and genetically witli the 
zona radiata of bony fishes is to be found in representatives of all the 
groups of fishes ; it is fugitive in Selachians and Lepidosiren, and 
probably in viviparous Teleosteans. The zona is produced by the ovum, 
not by the follicular cells, and is traversed in all cases by pore-canals, 
which rarely branch. An egg-membrane, genetically but not always 
structurally, comparable with the villous layer of Lepidosteus, is found 
in several other cases ; it, also, is produced by the ovum, and earlier than 
the zona. 
As to the function and history of the micropylar apparatus, the 
author suggests that the micropyle, being evidently a provision for the 
fertilization of the ovum, may owe its present structure to two tendencies 
which to some extent conflicted ; one was induced by the advantages of 
protection to the egg, the other by the necessity of some provision for 
the penetration of the fertilizing element. An optimum condition is 
reached when the penetrable area is reduced to a minimum, and that is 
the diameter of the head of a spermatozoon. The funnel may be a 
partial compensation for such reduction. The micropylar plug may 
mechanically determine the presence and form of a funnel. The micro- 
pylar cell may serve to form the canal by resorption, or to prevent the 
occlusion of the canal by less penetrable matter at the time of oviposition. 
Structure of Spermatozoa.f — Prof. G. A. Piersol discusses the 
structure of spermatozoa, and especially those of Ampliiuma tridactylum. 
In those of that Batrachian the tail presents the most interesting modi- 
fications. Starting with a sharply-cut transverse edge with a width of 
about 0*001 mm., it extends as a blade-like appendage to a length of 
0*2 mm., increasing to a width of 0*0018 mm. or more at the broadest 
part. The lower margin of the blade is formed by a relatively thick 
chief axial-fibre, while along the upper edge there is a secondary, thinner 
and shorter, fibre. When these fibres separate they are united by an 
extremely delicate but rigid membrane, which is perfectly smooth. 
Along the entire lower border of the chief fibre a beautiful gill-like 
membrane is attached, “ the graceful folds of whose free edge form a 
* Bull. Mus. Comp. Zool., xix. (1890) pp. 1-127 (9 pis.). 
t University Medic. Mag. Philadelphia, 1889, 20 pp. (sep. copy), 1 pi. 
