188 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
Embryology of the Sea Bass.* — Dr T. II. Morgan reports that 
those who desire a simple and straightforward account of the develop- 
ment of a single fish, from the egg to the time of hatching, will find it 
in Dr. H. V. Wilson’s account of the development of Serranus atrarius, 
pubFshed in volume ix. of the Report of the United States Fish Com- 
mission. The most interesting addition to our knowledge is the 
discovery that the ear, branchial sense-organs, and organs of the lateral 
line arise from a common structure or embryonic foundation. Before 
the closure of the blastopore there is, behind the eye, a long shallow 
furrow in the nervous layer of the ectoderm. At two points this furrow 
deepens, and at these two points the auditory sac and branchial sense- 
organs are ultimately formed. The posterior portion of the furrow is the 
foundation of the lateral line. 
Spermatogenesis in Myxine glutinosa.f — Mr. J. T. Cunningham 
has in consequence of Dr. Nansen’s criticisms, re-investigated the 
development of the spermatozoa of this protandrous hermaphrodite. 
He finds that the cells in unripe capsules are spermatocytes, which 
multiply by karyokinet'c division. At a certain period of development 
these cells cease to divide in this way, and commence to form spermato- 
zoa ; the nucleus of the spermatocyte loses its ordinary structure, and 
the whole of its chromatin is formed into a number, probably six or 
more, of pear-shaped bodies which may be called sperm-nuclei. By the 
activity of the protoplasm of the spermatoblast these nuclei separate one 
by one from the latter, passing out point foremost, and trailing a slender 
thread of protoplasm behind them. The thread breaks near the sperma- 
tocyte, and the free portion then forms the tail of a perfect spermatozoon. 
The author makes a critical comparison between the account he now 
gives and that which he first gave, and urges that there is no essential 
difference between them ; Nansen’s conjecture that originally each 
capsule contains a single large cell or spermatogonium is to some 
extent verified by a condition seen in the germinal proliferating tissue, 
where the separate germ-cells may be seen surrounded by stroma- 
cells. 
The mode of spermatogenesis in Myxine is, in many respects, unique, 
and resembles more closely that which occurs in certain Invertebrates — - 
Chmtopods and Molluscs — than that which occurs in higher Vertebrates. 
The most similar process has been described by Jensen for the Mollusc 
Triopa clavicjera. Mr. Cunningham uses the term spermatocyte in 
its etymological sense, and means by it the element which corresponds to 
what, in other cases, has been called a spermatogonium or spermatospore, 
which gives rise to a bundle of spermatozoa. 
The testicular follicles of Myxine are, in structure and development, 
much simpler than those of the more highly organized Invertebrates ; 
and, consequently, the history of the testis approximates very closely to 
that of the ovary ; and, in fact, the male and females are exactly, or 
almost exactly, homologous. W. Muller has shown that the testis of 
Petromyzon is composed of follicles and cells similar to those of the testis 
of Myxine. 
* Amer. Natural., xxv. (1891) pp. 1020-7. 
f Quart. Journ, Mier. Sei., xxxiii (18S1) pp. 1G9-86 (1 pi.). 
