ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
175 
The median bud undergoes modifications essentially similar to those 
which Mihalkowics has described for Mammals ; tho two lateral buds 
are temporarily united to tho median bud, but acquire independent 
relations with the brain, and separate from the main mass of the hypo- 
physis as two solid epithelial bodies. 
Origin of the Blood.* — Prof. C. K. Hoffmann has studied this in the 
yolk-sac of Selachians ( Acanthias ), and corroborates his previous con- 
clusion that the mesoblast has no share in forming the blood, but that 
blood and endothelium arise wholly and solely from the hypoblast. 
Some corpuscles appear to arise from the free nuclei of the yolk, which 
undergo fragmentation. But of greater importance is the remarkable 
process by which part of the hypoblast loses its epithelial character and is 
modified into the haemenchyme tissue from which blood and endothelium 
develope. The author emphasizes the likeness of this tissue to adenoid 
or reticular connective tissue, and just suggests the physiological interest 
of the hypoblastic origin of the blood. 
Development of Head of Gobius Capito.| — Mr. H. B. Pollard finds 
that, in this fish, the neural axis terminates at a point near the optic 
stalk, just as in the Salmon. An indentation and the arrangement of 
the cells at this point may be taken as indications of a neuropore. In 
later embryos there is evidence that the corpora striata belong to the 
upper part of the wall of the brain. The mouth and hypophysis arise 
as solid ingrowths of ectoderm, but there is nothing to show that the 
mouth was ever anything but a mouth. From a condensation of meso- 
derm round the ectodermic ingrowth of the mouth there arise the skeletal 
structures of both upper and lower jaws. 
Embryogeny of Selachii.j — Prof. P. Mitrophanow finds that the 
organs of the lateral line commence with a general thickening, along 
the sides of the head, of the epidermis ; the median part is detached 
below the hyoid arch to form the auditory lamella ; when this last is 
converted into the auditory pit, the parts of the hyoid and branchial 
arches become detached from the branchial thickening ; this happens in 
order from before backwards. When the conversion of the auditory pit 
into the auditory vesicle is accomplished, there is a further detachment 
of epidermic thickenings. The anterior part which separates from the 
thickening of the hyoid arch divides into two epidermic rod-like struc- 
tures which surround the eye ; these, later on, form the supra- and infra- 
orbital mucous canals. 
In connection with the general thickening of the hyoid arch a special 
thickening is formed which gives rise to the mandibular part of the 
lateral organs. Each branchial thickening undergoes a further dis- 
memberment and six branchial organs are ■ developed. Above each of 
these the part of the lateral organs is formed, and simultaneously with 
their development, there appear small suprabranchial nerve-branches. 
This lateral part gives rise to the lateral line of the trunk. 
The author concludes that the lateral organ in the Selachians studied 
is primitively formed by the germs of the mucous canal : — (a) supra- 
* Verh. K. Akad. Wetenschap. Amsterdam, iii. 4 (1893) 26 pp., 3 pis. 
t Quart. Journ. Micr. Sci., xxxv. (1894) pp. 335-52 (2 pis.). 
% Arch. Zool. Exper. et Gen., i. (1893) pp. 161-220 (6 pis.). 
