— 
— 
Normal Plates of the Development of Squalus acanthias. 73 
In 1892 H. E. ZıieGLER and F. ZiesLer!) published an account of a series of embryos of Torpedo 
ocellata selected to correspond with BaLrour’s stages “B”, “C”, “D”, “E”, “F”, “G”, “H” and an inter- 
mediate stage between “I” and “K”. (Table IX, column 6.) The well-known wax models of Torpedo 
from the atelier of F. ZIEGLER are based upon a careful study of fresh specimens and photomicrographs 
of “B”, “C”, “D”, “E—F” and “I-K” of this series. Besides photographic reproductions of these models the 
paper includes figures and descriptions of cross sections of the various stages. “H” and “I—K” are also 
figured as cleared specimens corresponding to BaLrour’s figures of these stages. From a comparison of 
BaLrour’s and ZIEGLER’s figures it would seem that the correlation is not a very exact one. “Stadium B” 
appears when compared with BaLrour’s plate to lie between “Stage B” and “Stage C”. ZIEGLER’S 
“Stadium C” likewise is farther advanced than BaLrour’s stage of that letter and probably lies between 
BALFoUR’s “C” and “D”. “Stadium D” is comparable to Barrour’s “E”, for the medullary folds are 
well raised both anteriorly and posteriorly. ZıEGLERr’s “F” is wholly unlike the embryo of the same 
letter figured by BaLrour, in which the cephalic plate is widely expanded and the caudal folds far 
separated. ZIEGLER’S figure is of an embryo with the anterior half of the medullary canal completely 
closed, the eye forming a prominent lateral swelling, one distinct gill pouch, and fifteen segments visible 
externally; it corresponds very well to BaLrour’s “G”, an embryo with seventeen segments. The author 
remarks that “F”, which is represented by an embryo of Pristiurus in BALFOUR’s series, is not well-marked 
in Torpedo. “Stadium G” is but little older than “Stadium F”, and probably should be placed between “G” 
and Hr, 
Hıs:) (Table IX, column 7, A and B) in 1894 contributed a second paper on the early development 
of elasmobranchs. He adopted BaLrour’s nomenclature of stages and gave a table, which is reproduced 
below, correlating the stages described in his earlier contribution with those established by BALFOUR. 
Tablke'Il. 
Tabulation of Hıs’ correlation of a series of embryos of Pristiurus and 
Seyllium with BALFOUR’s stages. 
Hıs’ series 
BALFOUR’s stages 
Embryo Length 
XXX 0,25 mm. A 
XXXVL O7 B 
xx IA 5, C 
I Se, D 
XXI 2 E—F 
XVII ZIODE, G 
Hıs also figures a series of nine embryos of Pristiurus, giving with them a table of measurements 
taken from the specimens when mounted in balsam. The general body development of the period 
covered by these stages is briefly described. In the normal plate correlation table this series has 
been placed under the sub-head “A” of the column given to this paper. Hıs’ table of measurements 
of the Pristiurus series and his correlation of its members with the BALFOUR series is given in the 
following table. 
ı) H. E. ZIEGLER and F. ZIEGLER, loc. cit. — ZIEGLER’s illustrations have been at least twice reproduced: 1902, 
F. KEIBEL, loc. cit. Fig. 6; 1902, H. E. ZIEGLER, loc. cit. Figs. 86, 88, 92, 97, 105. 
2) W. Hıs, Sonderung und Charakteristik der Entwicklungsstufen junger Selachierembryonen. Arch. f. Anat. u. Phys., 
Anat. Abt., p. 337—354, Taf. XXI, 18 figs. 
Normentafeln zur Entwicklungsgeschichte der Wirbeltiere. XII. Io 
