496 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
History of Sex-Cells in Cymatogaster.* — Prof. C. H. Eigenmann 
gives an account of the history of the sex-cells in the small viviparous 
fish Cymatogasler from the time of segregation to sexual differentiation. 
An account of the early history was published in the ‘Journal of Mor- 
phology ’ for 1893. 
The cells became located in the mesentery of the hind-gut in larvae 
2*5 mm. long, but did not divide until the 7 mm. stage. They migrate 
laterally, and are mixed with a few cells of peritoneal origin, which give 
rise to the entire stroma of the reproductive organs. The sexes can 
first be distinguished after about eleven segmentations from fertilisation. 
A small groove on the outer ventral part of the sex ridge is the first 
indication of the ovarian cavity, and is the surest criterion of the female. 
The reason for the determination of sex remains unknown. 
Transient Hervous System in Skate.f — Dr. J. Beard gives in this 
paper an account of some of his investigations into “ the transient nervous 
apparatus of certain Ichthyopsida.” The present contribution deals 
with a series of about 120 skate embryos ( Baja hatisf from 5 mm. to 
19 cm., and is a continuation of previous work on Lepidosteus osseus. 
The first part of the paper describes the development and degeneration 
— the Werden and Vergehen— of a transient apparatus of ganglion-cells 
and simple nerves. Its probable functions and fate are then discussed. 
At the close of the paper the question of antithetic alternation of genera- 
tions, or “ development by substitution of organisms,” is discussed, and 
“ an attempt is made to prove that such an alternation can be traced in 
Vertebrate development, more especially in that of lower Vertebrates 
like Baja.” We follow the author’s summary of his work. 
Development of the ganglion-cells of the apparatus. — When sections 
of early embryos (5 mm.) are examined, especially in the region of the 
pronephros and for some distance behind this, at a period when the cells 
of the future spinal ganglia are wandering out from the lips of the cord, 
there appear among these and on the cord itself certain cells in the act 
of assuming ganglionic characters. By the time all the gill-clefts are 
formed, the region of the cord for about 25-26 somites posterior to the 
front of the pronephros has a tesselated roof of ganglion-cells. There 
may be 2-8 in a single transverse section, about 20 in a somite, perhaps 
500-600 altogether. Most, if not all, of these central ganglion-cells are 
multipolar, and lie in a close meshwork of their processes. The portion 
first developed is subsequently somewhat reinforced by cells arising 
further back, even to the tail-end. The explanation suggested for the 
feebleness of this posterior portion is that it is due “ to a carrying-back 
of parts of a larva (represented by the blastoderm) into a region far 
beyond the blastodermic limits, owing to the raising-up of the embryonic 
body from the blastoderm and its growth backwards.” 
Peripheral ganglion- cells of the transient system. — This title is used 
to describe those ganglion-cells which do not lie at the top of the spinal 
cord, but are met with either in the mesoderm or in the myotomes, or 
just underneath the epiblast. One frequent feature in those cells which 
migrate from among the elements of the future spinal ganglia is their 
* Trans. Amer. Micr. See., xvii. (1896) pp. 172-3. 
f Zool. Jakrb. (Afith. Anat. Ontog.), ix. (1896) pp. 319-426 (8 pis.). 
