470 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
canals may be connected by median commissures with their fellows of 
the opposite side. In Gadus the canals have only diverged slightly 
from the typical form, the sense-organs are somewhat reduced, and Savian 
organs and Lorenzini’s ampullas are absent. The lateral line system 
of Fishes is not metameric, and the nerves supplying the lateral sense- 
organs form a separate series in themselves and are not connected 
with any of the other cranial nerves. The so-called lateralis nerve 
of Petromyzon is not a lateral line nerve at all, but belongs to the 
lateralis accessorius system. The lateral line sense-organs of Fishes 
and Amphibia are not homologous with the lateral sense-organs of 
Annelids. The sensory canals were probably represented in the ancestral 
Vertebrates by superficial non-segmental sense-organs. These, together 
with certain lateral glandular organs, sank below the surface, and fused 
to form canals filled by mucus secreted by the glandular organs. These 
glandular organs have become reduced in importance, and their function 
is now to secrete a substance corresponding to the endolymph of the ear. 
The primitive sensory canal system was probably confined to the region 
now occupied by the ear, and it gave rise alike to the existing lateral 
line system and to the auditory organs. The author believes that the 
semicircular canals of the ear are homoplastic and not homologous with 
the sensory canals. 
Absence of Parietal Eye in Myxine.* — Herr F. R. Studnicka 
publishes a short note on this subject. He quotes various authors to 
show the difference of opinion which exists as to the presence or absence 
of the pineal eye in the hag. Thus Beard describes it in one specimen 
among many examined, while Leydig doubtfully notes a structure which 
may be a true pineal gland or else a lymph-sac. The author himself 
finds that the parietal organ is entirely absent ; the structure described 
by Beard is the infundibular prolongation of the thalamencephalon ; that 
described by Leydig is not a part of the brain but probably an enlarged 
lymph-sac. In the total absence of the parietal organ, the brain of 
Myxine is contrasted with that of Petromyzon , where there is a distinct 
pineal eye at the end of a well-developed epiphysis. 
Relation of Yolk-elements to the Blastoderm-Cells.f — Prof. M. 
Lavdowsky and Dr. N. Tischutkin have studied this problem in chick 
embryos, and their general conclusion is that the elements of the white 
yolk, which the authors call Dottercyten, are the main elements for 
the three germinal layers, in fact that these cytode-like bodies of the 
yolk furnish all the subsequent nucleated cells of the blastoderm. The 
chief or primitive layer of the blastoderm is the upper multicellular 
layer, which is a veritable “ archiblast,” to use the term proposed by 
His. The Dottercyten are derivatives of the yellow yolk, arising from 
characteristic clumps — the yolk-segments — whose rich proteid substance 
furnishes chromatin. There are no sharp microscopic or physiological 
differences between the two kinds of yolk. Although the authors do 
not wish to run a tilt against Virchow’s conclusion “ omnis cellula e 
cellula” nor against its modern corollary i: omnis nucleus e nucleo 
they maintain that cell-development and cell-multiplication may occur in 
several distinct ways, including that above indicated. 
* SB. Bohmisch. Ges. Wiss., 1898, pp. 1-4. 
f Biol. Centralbl., xix. (1899) pp. 411-21. 
