ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
605 
higher Vertebrates, since it occurs inside the peritoneal sheath, and not 
along with it. The spiral fold or valve represents the apposed walls of 
adjacent twists, the interior being filled with mesenchyme, and is not 
merely a longitudinal fold of mucous membrane twisted in a spiral. 
In some Selachians ( Carcliarias , Zygoena, &c.) the fold is straight, 
and here, as in the anterior part of the gut in Pristiarus, there has been 
spiral coiling without spiral twisting. In Chimsera more than the 
anterior half is coiled, the rest twisted. The initial stage of both may 
be seen in embryos of Pristiurus. 
Sex-Differentiation in Cymatogaster.* — Prof. 0. H. Eigenmann 
has endeavoured to trace the history of the reproductive cells in this 
viviparous Teleostean from their first appearance until sexual differen- 
tiation, noting the changes, if any, from one cell-generation to another. 
The sex-cells are segregated very early, before any protovertebrae 
are formed. From their size they seem to be of the fifth generation or 
thereabout. Their number (9-23) remains unchanged from the time of 
segregation until the larva has readied a length of 7 mm., except that 
four are lost. The cells migrate backwards in early stages ; the two 
sides are not symmetrical. No somatic cells are ever transformed into 
sex-cells, nor (except the four which are lost ?) are sex-cells changed into 
somatic cells. The sex-ridges are first formed posteriorly, and consist 
of two folds of the peritoneum with included elements. A rhythm of 
division is kept up for some time by the descendants of each sex-cell. 
The ovarian cavity is formed by the union, from in front backward, 
of ridges of peritoneum bounding grooves at the upper outer and lower 
outer margins of the ovary. The anterior part of the oviduct has a 
similar origin, with the difference that the lower outer grooves of the two 
ovaries meet, producing a long slit in the thickened part of the meso- 
rectum before the upper and lower ridges have had time to unite. The 
vas deferens is not homologous ; it is lined with stroma cells of the 
testis, from which it arises. The sexes are nearly equally distributed. 
Sex cannot be due to position in the ovary, to age of spermatozoa, to 
condition (age) of the ovum, to relative amount of nutriment, to kind 
of food, to relative amount of oxygen, or to relative rate of growth ; in 
fact, the determinants are not known. “ The ultimate sex-cells are due 
to the process of histogenesis entailed by the division of labour. They 
bear the same relation to the entire corm as any other series of tissues, 
and their origin is to be explained in the same way.” 
So-called Suprarenals in Cyclostomata.f — Messrs. W. E. Collinge 
and Swale Vincent find no satisfactory evidence of suprarenal bodies in 
Cyclostomata. The bodies described as such by Ecker are simply con- 
nective tissue ; so are the “ white-bodies ” and “ bullet-shaped bodies ” 
of Ratkke. The body described by Johannes Muller as suprarenal, and 
later as thymus, is the pronephros, present in Myxine and Bdellostoma , 
but absent in the lamprey. There is no evidence of relation between 
suprarenal bodies and renal organs. The suprarenals, still undemon- 
strated in Cyclostomata and Dipnoi, increase in importance as we ascend 
the Vertebrate series, and cannot therefore be regarded as vestigial. 
* Arch. Entwickmech., iv. (1896) pp. 125-79 (6 pis. and 1 fig.). 
f Anat. Anzeig., xii. (1896) pp. 232-41 (2 figs.). 
