Normal Plates of the Development of Squalus acanthias. 71 
Although several series of elasmobranch embryos were figured and partially described!) prior to 
the Leypic’s contribution, with which this table begins, the data presented by them seemed toßmeager to 
admit of a correlation of value. The second part of Levoıc’s Beiträge zur mikroskopischen Anatomie und 
Entwicklungsgeschichte der Rochen und Haie?) (Table IX, column 2) contains an account of the egg and 
segmentation of Pristiurus and a description of a series of four embryos of Squalus acanthias of 7", 1", 2" and 3" 
respectively. The youngest embryo of the series is described in detail, the account including a description 
of the viscera, notochord, vascular system, brain and gill slits. A figure of this specimen seen as a transparent 
object is included in the plates. The external anatomy of the remaining members of the series is figured 
and there is a general account of the development of the notochord, gill slits, lateral line, urogenital system 
and skull. 
Hıs®) in 1876 (Table IX, column 3) published a careful study of a number of young embryos of 
Pristiurus and Seyllium. The series consists of twelve stages representing the development from a slight 
thickening of the posterior rim of the blastoderm to a period when only the middle two-fifths of the embryo 
is attached to the blastoderm and twenty-seven pairs of segments and three gill slits are present. Eight of the 
twelve stages are illustrated by excellent figures, the magnification of which is given in connection with the 
plate. A very complete set of measurements of the embryos after fixation is included in the paper. In a 
second contribution which appeared in 1894 Hıs has correlated this series of embryos with BALFOUR’s stages ®). 
The “stages” (Table VIII, column 4) established by BaLrour have become so incorporated in the 
literature of elasmobranch embryology that they are considered here in some detail. A section of BALFOUR’s 
work upon the embryology of elasmobranch fishes’) contains figures and descriptions of a series of 
some seventeen embryos, ranging in development from the segmented blastoderm to a stage when “the 
head resembles that of an adult fish”. These stages the author designated by a series of letters “A” to 
“O” inclusive, there being no stage “J”, and throughout the remainder of the work the statement of the 
“stage” is used to indicate the general state of development of the embryo. This series is made up of 
several species of elasmobranchs. Stages “A”, “B”, “C”, “D”, “E”, “F”, “H”, “T’ and “K” are represented 
by embryos of the sawfish Pristiurus; “G” by Torpedo; “L”, “M”, “N”, “O”, “P” and “Q” by the European 
dog fish Seyllium canicula. The mode of preparation of the figured specimens in also not always the same. 
The figure of stage ““B” represents a fresh unfixed blastoderm. “G”, “H” and “I” are figures of embryos 
“viewed as transparent objects” and also represent living specimens; the remaining figures are of embryos 
fixed in chronic acid. The figures of “A” to “F” inclusive are dorsal views; “G”, “H” and “I” are lateral 
views of transparent specimens; “K”, “L”, “N” and “O” are seen in lateral view, and the ventral surface 
of the head and pharyngeal region of each of these specimens is shown in a separate drawing on a larger 
scale. Only the head and pharyngeal region, as seen in lateral view, is figured for stages “M”, “P” and 
“Q”,. No scale of magnification is given in BALFOUR’s work, but a study of the figures shows that it has 
been changed at least three times in the course of the series. 
I) Among these may be mentioned: 
1834 Davy, J., Observations on the Torpedo. Trans. Roy. Phil. Soc. London, p 531—550. 
1867 WYMAn, S., Observations on Raia batis. Mem. Amer. Acad., Vol. 9, 1867, p. 31—44, I pl. 
1850 LEUCKART, R., Ueber die allmähliche Bildung der Körpergestalt bei den Rochen. Zeitschr. f. wiss. Zool., Bd. 2, p. 254—267, 
Taf. XIV. 
2) F. LEvDIG, Beiträge zur mikroskopischen Anatomie und Entwicklungsgeschichte der Rochen und Haie, 127 pp., 4 Taf., 
8°, Leipzig 1852. 
3) W. Hıs, Ueber die Bildung der Haifischembryonen. Zeitschr. f. Anat. u. Entw., Bd. 2, p. 108-124, Taf. VII. 
4) See review of this paper on p. 73. 
5) F. M. BALFOUR, The development of elasmobranch fishes. From B to G. Journ. Anat. and Phys., Vol. Io, p. 672, 
688, Plate XXIX. 
