Normal Plates of the Development of Squalus acanthias. 43 
Descriptions of Figures of Reconstructions and Dissections. 
A number of illustrations of dissections and reconstructions of embryos of Squalus acanthias are to 
be found scattered through the literature of elasmobranch development‘). These are, however, in most 
cases, illustrations of particular organs or systems and include only a limited series of stages. It has been 
thought that a series of figures showing general development of this form would be of value, and for that 
purpose the following graphic reconstructions, made from selected embryos of the normal plate series, have 
been added to the customary plates. There are included also figures of a short series of dissections of 
embryos selected with care to correspond with some of the later stages. 
The general plan adopted has been to reconstruct all the important structures of the embryo 
as seen from the left side, with the skin and mesodermal structures — with the exception of the vascular 
system — removed. It has been necessary, however, to modify this plan in several particulars, and in 
connection with some embryos to introduce supplementary reconstructions. Thus the mesoderm has been 
included in the reconstructions of the first four embryos and mid-sagittal section views of embryos 
of 2.7 mm. and 3.5 mm. in length (N.P.S. 9 and N.P.S. 14) have been added. The arterial system and 
the heart are included in all the general reconstructions of embryos over four millimeters in length. The 
1) Among these may be mentioned those of: 
a) The central nervous system. 
Jo#NsTon, J. B., 1909, The morphology of the forebrain vesicle in vertebrates. Journ. comp. Neur. and Psych., Vol. 19, p. 457—539- 
v. KUPFFER, K., 1906, Die Morphogenie des Zentralnervensystems in HERTWIGs Handbuch d. vergl. u. exp. Entw. d. Wirb. 
Locy, W. A., 1895, Contributions to the structure and development of the vertebrate head. Journ. Morph., Vol. II, p. 497594. 
— 1899, New facts regarding the development of the olfactory nerve. Anat. Anz., Bd. 16, p. 273—290. 
— 1903, A new cranial nerve in selachians. Mark Anniversary Volume, p. 41-54. 
Near, V. H., 1898, The segmentation of the nervous system in Squalus acanthias. Bull. Mus. comp. Zool. Harvard Coll., Vol. 31, 
p- 147294. 
b) The peripheral nervous system. 
BROHMER, P., 1909, Der Kopf eines Embryos von Chlamydoselachus und die Segmentierung des Selachierkopfes. Jena. Zeitschr. 
f£. Naturw., Bd. 44, p. 647—698. 
JotnsTon, J. B., 1909, loc. cit. 
Locy, W. A., 1895, loc. cit. 
— 1809, loc. cit. 
— 31003, 1062 cit; 
— 1905, On a newly recognized nerve connected with the fore-brain of selachians. Anat. Anz,, Bd. 26, p. 33-123. 
MEEK, A., 1909, The encephalomeres and cranial nerves of an embryo of Squalus acanthias. Anat. Anz., Bd. 34, p- 473—475- 
NEAL, V. H., 1898, loc. cit. 
PLATT, J., 1891, A contribution to the morphology of the vertebrate head. Journ. Morph., Vol. 5, p. 79-112. 
c) The nasal pit. 
BERLINER, K., 1902, Die Entwicklung des Geruchsorganes der Selachier. Arch. f. mikr. Anat., Bd. 60, p. 336-405. 
d) The head somites. 
BROHMER, P., 1909, loc. cit. 
LAMB, A. B., 1901, The development of the eye muscles in Acanthias. Amer. Journ. Anat., Vol, I, p. 185—202. 
PLATT, J. B., 1896, loc. cit. 
f) The urogenital system. 
GREGORY, E. R., 1897, Origin of the pronephric duct in selachians. Zool. Bull., Vol. I, p. 123—129. 
MinoT, C. S., 1892, Human embryology, p- 236. [Mesonephric tubule.] 
g) The vascular system. 
HOCHSTETTER, F., 1906, Die Entwicklung des Blutgefäßsystems. HERTwIGs Handbuch d. vergl. u. exp. Entw. d. Wirb., Bd. 3, 
TI. 2, p. 21—166. 
PLATT, J. B., 1896, loc. cit. 
h) The skull. 
SEWERTZOFF, A. N., 1899, Die Entwicklung des Selachierschädels. Festschr. v. KUPFFER, p. 281—324. 
6* 
