ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
695 
of the vessels themselves ; they are true cells, at first spherical in shape 
and laden with yolk-granules. 
The dorsal aortce are, with the exception of the vitelline veins and 
the heart, the first vessels to appear. They arise on each side as a 
number of isolated lacunar spaces along the roof of the pharynx, which 
open into one another and so form continuous vessels. In each 
branchial arch there appears a lacunar efferent vessel at the level of 
the external gill ; this extends dorsally, meets and opens into a diver- 
ticulum of the dorsal aorta. Immediately behind the efferent vessels, 
at the level of the gill, an afferent vessel appears; this is also lacunar 
and at first independent. After describing in detail the development 
and fate of the vessels the authors point out that throughout the early 
stages of development there is a striking resemblance in arrangement, 
relations, and proportions between the arterial and venous systems of the 
tadpole and those of an adult Elasmobranch. The external and internal 
gills apparently form one continuous series of structures. The tadpole 
undergoes a distinct increase in bulk before the opening of the mouth, 
and it is suggested that in the early stages, nutriment is absorbed 
through the sucker. 
Process of Maturation in Ova of Selachians.* — Prof. N. Kast- 
schenko points out that the process of maturation of meroblastic eggs has 
not yet been clearly made out. In one thing only have all investigators 
agreed, and that is that the germinal vesicle passes to the animal 
pole of the egg, and then finally disappears. The formation of polar 
globules was not, as a rule, observed, and was consequently denied, while 
no explanation was given as to whence came the ovarian nucleus. 
Comparatively recently, the admirable work of O. Schultze on the 
process of maturation in the Amphibian egg has thrown much light 
on the subject. Although the author’s observations are not complete 
they are, he thinks, sufficient to justify us in concluding that the 
process of ripening of the Selachian egg is, in all its primary phenomena, 
exactly comparable to that of holoblastic eggs. During maturation the 
polar globules are formed by karyomitotic division of the egg-cell ; of 
the two one is separated off in the ovary and the other probably at 
the time of fertilization. The germinal vesicle, as a whole, is certainly 
not expelled from the egg, though some of its constituents may be. 
Prof. Kastschenko has not observed the granular coagulum noticed by 
several observers, and he thinks it much more probable that the fluid 
contents of the germinal vesicle, as well as its membrane, are simply 
dissolved in the yolk of the egg. The chromatin filaments of the 
polar spindle of the globules and of the ovarian nucleus are the same 
chromatin filaments (or their descendants) as are to be seen in the resting 
germinal vesicle long before the maturation of the egg. 
Development of Teleostean Fishes.! — Dr. R. Fusari describes the 
first stages in the development of Cristicejps anjentatus , and bases on his 
observations a number of conclusions. During the first stages of 
segmentation the perivitelline membrane continues to yield elements to 
the blastodisc, but later on, when the merocytes no longer remain as 
* Zeitschr. f. Wiss. Zool., 1. (1890) pp. 428-42 (1 pi.). 
f Atti R. Accad. Lincei— Rend., vi. (1890) pp. 70-8. 
