284 
E. W. MACBRIDE. 
Lwoff had based his conclusion that ectoderm cells ai’e inflected 
round the dorsal lip of the blastopore on his observation of 
numerous mitoses there ; he asserted that they were wanting 
elsewhere. On this point Sobotta joins issue with him, and 
points out that mitoses occur frequently in all parts of the 
archeuteric wall. Sobotta had not been able to accurately 
determine the orientation of his embryos, but Samassa, who 
wrote in the same year (29), using the method of double 
embedding in celloidin and paraffin, was able to determine 
this. Samassa’s results in general confirm Sobotta’s, but they 
add several most important points. He points out that mitoses 
take place at regular intervals in both endoderm and ecto- 
derm, so that it is quite possible in one embryo to find no 
mitosis at all, and in another of nearly the same size to find 
numerous mitoses. Samassa further asserts that the blasto- 
pore closes by the synchronous approach of all its sides, and 
he rejects utterly the idea that it closes in a longitudinal 
seam. With regard to the formation of the mesoderm he 
confirms Hatschek’s results; he points out that the longi- 
tudinal grooves which give rise to the mesoderm make their 
appearance before the nerve-plate becomes invaginated, and 
that therefore Lwoff’s explanation of their formation is 
groundless. Klaatsch’s paper on the gastrulation (20) contains 
several admirable new points. He remarks that the abundance 
of mitoses found by Lwoff in the neighbourhood of the dorsal 
lip of the blastopore does not prove an inflection of cells 
round this lip, but rather proves that here is to be found a 
growing point from which new cells are added to both 
ectoderm and endoderm. He denies the possibilit}' of an 
inflection of cells round the dorsal lip, because of the difference 
in histological character between the ectoderm and the cells 
forming the doi-sal wall of the archenteron. With regard, 
however, to the ventral lip, he infers that here there is a 
genuine inflection of cells, because he found outside this lip 
large rounded cells, which in later gastrulm were replaced by 
small-celled ectoderm. My own paper (26) was published in 
ignorance of the results of the three workers whose observa- 
