622 
Proceedings of Royal Society of Edinburgh. [sess. 
On Duplicitas Anterior in an Early Chick Embryo. 
By Thomas H. Bryce, M.A., M.B. (With Four Plates.) 
(Read June 19, 1899.) 
The literature of Duplicity in Birds affords, out of a total of 
about ninety-five recorded cases of multiple formations of all kinds 
on a single blastoderm, from the stage of the primitive streak to 
the fourth day of incubation, only a small proportion of instances 
of “ duplicitas anterior.” Dareste (i.) in his atlas figures three ; 
Gerlach (ii.) adds representations of three others — one case of his 
own, a second originally described by Ahlfeld, and a third by 
Beichert ; Klaussner (iii.) gives a seventh case ; and Bianchi (iv.) 
describes a monstrous embryo at a later stage (P5 cm. in length). 
Most observers have been content with the partial information 
derived from the study of the whole object, and only three 
embryos of this class, which have been studied in serial sections, 
have been described : — 
1st. Erich Hoffman’s (v.) with three somites, 
2nd. Mitrophanow’s (vi.) with six somites. 
3rd. Kaestner’s (vii.) with seven somites. 
The present case makes the fourth. It lies in point of develop- 
ment intermediate between Hoffman’s embryo and Kaestner’s, and 
in general features it closely resembles them, hut differs from 
Mitrophanow’s in the greater symmetry of the components, for 
in his case, one member was considerably further developed than 
the other. 
Thus, anterior duplicity is comparatively rare in birds, although 
it is the universal form in fishes, and the general form in reptiles 
and amphibians. Among the domestic mammals it is not un- 
common, hut the only case of the condition at an early stage, 
which has been studied by the help of serial sections, is an early 
human derodyme of 18 mm. described recently by Laguesse and 
Bue (viii.). 
The embryo which is the subject of this communication was 
obtained from an egg which had been incubated for thirty-four 
