Introduetion. 
The normal plates of Acanthias were undertaken in 1896, when the series was first planned by 
Professor KEIBEL. Originally the work was assumed by myself and the late Dr. ALFRED SCHAPER, who 
was at that time a member of my laboratory staff. I at once proceeded with the collection of the material, 
the making of drawings and the preparation of the serial sections. As Squalus acanthias is abundant on 
the New England coast, it is caught in large numbers by the fishermen, who are glad to bring the fish in 
for a small price, as they have no market value. It is therefore possible to obtain during the summer an 
almost unlimited supply of “candles” as the fishermen call the egg-cases, with ova in all stages of develop- 
ment from segmentation up to those with embryos of about 50 cm. in length. 
The drawings were made, with the exception of a few added later, by Dr. Epwın A. LockE of 
Boston. They are remarkable for their fidelity to the specimens and the beauty of their execution. The 
importance of the Elasmobranchs for embryological research, since the classic researches of BALFOUR, has 
steadily grown. In consideration of their importance it seemed to me be desirable to add to the series of 
side views, a certain number of dorsal and ventral views of selected stages of our type. To this extension 
of the programme the editor and publisher have generously consented. I trust that those, who use the plates, 
will welcome the additional figures. 
Dr. SCHAPER’s return to Germany in Igoo precluded his participation in the work and I found myself 
unable to complete it alone. The matter remained in abeyance until the task was assumed by Dr. SCAMMON 
in 1907. Some progress had been made with the bibliography, but he has completed it by considerable 
labor. His work on the embryos has been based entirely upon the 121 series of sections of Acanihıas 
embryos in the Harvard Embryological Collection. The series have not been made at random, but by 
a carefully followed plan — in general of each stage there are three specimens nearly ıdentical in length 
and cut respectively in the transverse, sagittal and frontal planes. 
The reconstructions of the anatomy of the pig embryo of 12.0 mm. by Professor FREDERICK T. LEwiıs, 
which have been inserted in my Laboratory Text-book of Embryology had demonstrated to us the great 
value of such pictures. Professor LEwIs urged the desirability of adding reconstructions to the normal 
plates. Dr. Scammon, despite the great amount of work involved, undertook to make them. His success in 
this laborious task will be appreciated by all who consult the present volume. As the figures were to be in 
black and white we found it necessary to study carefully all the possible devices for varying the textures, so as 
to render the various structures perfectly distinct. I think good success has been attained in solving this special 
technical problem. The pen drawings were made by Mr. W. T. OLivEr of Lynn (Massachusetts). The high 
quality of his work is shown in the figures. It seems to me that the reconstructions enhance the value of 
the normal plates so greatly, that it is to be hoped they will form an indispensable requirement hereafter. 
In conclusion it should be stated clearly that the credit and responsibility for the text and ihe 
anatomical reconstructions of this work belong entirely to Dr. SCAMMON. 
Harvard Medical School Boston, Mass., 
October 20, IgIO. 
Charles S. Minot. 
Normentafeln zur Entwicklungsgeschichte der Wirbeltiere. XII. I 
