FORMATION OF GERM-LAYERS IN CRANGON VULGARIS. 343 
The Formation of the Germ-layers in Crangon 
vulgaris. 
By 
Ww. F. R, Weldon, M.A., F.R.S., 
Fellow of St. John’s College, Cambridge ; Jodrell Professor of Zoology in 
University College, London. 
With Plates XX, XXI, and XXII. 
Tue development of the common shrimp has recently been 
studied by Kingsley,’ whose papers contain full references to 
the work of other authors on Crustacean embryology. To 
these, and to the memoir of Nusbaum * on the development of 
Mysis, the reader is referred for an account of the literature 
of the subject. 
Professor Kingsley’s account of the later development of 
many important organs, especially of those of mesoblastic origin, 
is somewhat meagre; I hoped, during a recent visit to the 
Laboratory of the Marine Biological Association at Plymouth, 
to supplement his work by observations on the later history of 
the mesoderm. A preliminary study of the mode of forma- 
tion of the germinal layers has, however, led me to form a 
conception of the early development of Crangon which 
differs widely from that arrived at by Kingsley. My observa- 
tions on the early stages are, therefore, described in what 
follows. 
Embryos of various stages were obtained by the examination 
of newly-caught females; any attempt to rear the eggs in 
1 *Bulletin of the Essex Institute,’ xviii, p. 99,and xxi, p.1, Salem, Mass., 
1886 and 1889. 
2 * Archives de Zoologie Expérimentale,’ v, 1887. 
