ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
725 
Development of Hepatic Vessels and Blood-corpuscles in Anura.* 
— Prof. J. Nusbaum finds that the endothelium of the first hepatic 
capillaries has a double origin : — from those yolk-entoblast cells which 
form the blood-corpuscles, and from the endothelium of the primitive 
vitelline veins with which the first hepatic capillaries communicate. 
But in reality the endothelium of the vitelline veins and of the heart is 
formed in Amphibia from endoblastic elements. Nusbaum believes that 
the endodermic origin of the blood-corpuscles is the primitive condition 
in Vertebrates, and the mesodermic origin a secondary modification. 
Development of Scales of Lepidosteus.f — Mr. W. S. Nickerson 
remarks that from the Selachian type on there has been a constant 
tendency towards reduction of superficial parts (spines), and increase of 
the deeper parts which are independent of the epidermis. In Selachians 
the process of scale- formation begins at the surface of the dermis just 
beneath the basement membrane. In Ganoids there is the same process 
as at the base of the epidermis, but in a much less vigorous manner, 
while the principal activity is in the midst of the dermis. In the higher 
Teleosteans the whole scale-growth is dermal, and the more superficial 
process is entirely lost. 
The author believes that the ganoin layer of the scale is found only 
in Ganoid fishes among Vertebrates, and he urges that the only relation- 
ship between the scales of Lepidosteus and teeth is such as arises from 
the fact that both are derived from an ancestral condition similar to that 
found in the scales of Selachians. To-day, each represents only a highly 
modified part of the early ancestor. 
Segmentation in Petromyzon marinns.J— Mr. C. F. W. McClure 
finds that the third plane of cleavage is not equatorial, but, as in the 
Ctenophora, consists of two meridional furrows ; he gives a careful 
account of the observations made to assure himself that this marked 
divergence from the normal segmentation of Vertebrates occurred with 
great regularity. And, though he recognizes that it has no morpho- 
logical significance, he thinks the facts should be recorded. 
Development of Nervous Tissue.§— Prof. G. Valenti describes the 
development of the nerve-cells and neuroglia in cartilaginous fishes — 
Mustelus vulgaris , Torpedo ocellata, &c. His results tend to show : (a) 
that the ectodermic elements forming the medullary canal give origin to 
cells of the neuroglia as well as to nerve-cells ; (b) that at an early 
stage embryonic connective elements insinuate themselves, and probably 
become cells of the neuroglia ; (c) that insinuated connective cells or 
leucocytes from the pia mater take part in the formation of the neuroglia 
of the adult ; (d) that there are thus two kinds of neuroglia, one of con- 
nective origin and of exclusively supporting function, the other of 
ectodermic origin and probably of more than supporting function. 
P. Histolog-y. 
White Corpuscles of Mammals. ||— Herr 0. Van der Stricht finds, 
from a careful examination of the various hsematopoetic and lymphoid 
* Biol. Centralbl., xiii. (1893) pp. 356-9. 
t Bull. Mus. Comp. Zool., xxiv. (1893) pp. 115-40 (4 pis.). 
X Zool. Anzeig., xvi. (1893) pp. 367-8 ; 373-6 (3 figs.). 
§ Atti Soc. Toscana Sci. Nat. Pisa, xii. (1893) pp. 75-98 (1 pi.). 
H Anat. Anzeig., viii. Erganz. Heft (1893) pp. 81-92 (11 figs.). 
