Normal Plates of the Development of Squalus acanthias. 27 
In December of last year there appeared a paper by UnGARo!) in which is proposed a new set of 
subdivisions of the period of development preceding BaLrour’s “Stage L”. As indicated by their nomen- 
clature, these subdivisions are based in the main upon changes in structure and to only a slight extent 
upon external appearance. UnGAro’s work is based upon a study of Pristiurus melanostomus. FHlis correlation 
of the proposed subdivisions with the BaLrour stages (as modified by Hıs und the ZIEGLER’) is re- 
produced below. 
Table WII, 
Tabulation of UNGARO’s correlation of his proposed stages with those of BALFOUR 
(as modified by Hıs and the ZIEGLERS). 
UNGARO’s stages BALFOUR’s stages 
I Fase di segmentazione o 
preembrionale 
1° periodo — di gastrulazione 
h ’ propriamente detta A 
ABS Ha SRH Zone I, Ei IV. 
2° periodo — mesodermico B 
III Fase iniziale di organo- 
= C-D-E 
genesi (neuro-cordale) 
1° periodo — della formazione 
del canale neurenterico 
IV. Fase del pronefro o 2° periodo — di evoluzione 
branchiale del pronefro ER 
3° periodo — di involuzione 
del pronefro 
Description of general correlation table. 
(Table IX.) 
The general purpose of this table has already been described. The normal plate series and the 
series of the ten papers considered above have been arranged in vertical columns. A horizontal column 
has been assigned to each member of the normal plate series. The members of the other series have been 
arranged under their respective columns each in the space of the normal plate stage with which it seemed 
to best correspond. In some cases the symbol of stage is preceded by a bracket which includes two or 
more spaces of the normal plate stages. Such an arrangement indicates that the stage thus represented 
possesses characters common to the several inclosed normal plate members. Stages of other authors which 
apparently lie between two members of the normal plate series are placed in the line intervening between 
their spaces. A question mark follows the designation of those stages whose correlation seemed parti- 
cularly doubtful. 
In many cases the author has used some symbol, letters or figures, to designate his stages and these 
symbols have been employed in the table. When such was not the case, the number of the figure which 
illustrates the embryo in the original publication is used for this purpose. 
Besides the number of each stage there are included in separate columms under the normal plate 
heading the length, number of segments, and numbers of the embryos in the Harvard embryological col- 
lection. The number of somites in the last three instances has been determined from cleared specimens of 
the same stage and is therefore only approximate. 
I) 1910, V. UNGARO, Studi sullo sviluppo dei Selaci (Pristiurus melanostomus Bp.), Anat. Anz., Bd. 37, p. 636—644. 
