1896.] Embryology. 597 
EMBRYOLOGY. 
Protoplasmic Continuity.—Prof. Hammar, of Upsala,’ empha- 
sizes by figures and description the connection of the cells of the egg of 
a cleaving sea urchin known to Selenka and others, but hitherto re- 
garded as of no importance. He finds a thin outer layer on the cells 
of the early and later cleavage cells and even on the cells of the blas- 
tula. This layer is seen both in living and in preserved and sectioned 
material. Its appearance is not that of a membrane but, the author 
thinks, rather that of an “ ectoplasmic” outer part of the protoplasm 
of the cell. This outer layer is very thin and might be easily over- 
looked. 
It extends continuously over the entire egg and as it seems to be a 
part of each cell, all the cells are thus held together by a continuous 
outer pellicle that the author thinks is a protoplasmic layer. 
This actual connection of the cells at their outer surfaces, if really a 
protoplasmic connection, should, as the author insists, be of great im- 
portance in the interpretation of the results of experimentation upon 
echinoderm eggs. He suggests that it offers a suggestion towards the 
explanation of the interaction believed to exist between the cells of a 
cleaving egg. Moreover such a connection would make clear why very 
different results have been obtained after shaking eggs and separating 
the cells more or less. 
Cell Studies in Annelid Eggs.—Prof. E. Korschelt, of Mar- 
burg,’ has made a most detailed and thorough study of the maturation 
and fertilization of the eggs of the small polychxtous annelid, Ophryo- 
trocha puerilis with special reference to the number of chromosomes 
concerned in cell divisions at different phases of the life history. 
Many of the interesting facts described cannot be here referred to, 
but only some of those that bear upon the question of the value of 
chromosomes as permanent individuals. 
The number of chromosomes found in dividing cells in the adult is 
four, in certain ectodermal, entodermal and mesodermal structures. 
This same number is found in the cells of the ovary and of the testis, 
the ancestors of the eggs and sperms. The same number is found in 
‘Edited by E. A. Andrews, Baltimore, Md., to "n abstracts reviews and 
preliminary notes may be sent. 
? Archiv f. mik. Anat., Marz 2, 1896. 
* Zeit. f. wiss. Zool. 60, Dec. 31, 1895, pps. 543--680, pls. 28--34. 
