198 ADAM SEDGWICK. 
forward in two bands—one on each side—between the ectoderm 
and endoderm (Pl. XIV, figs. 26 a@ and 5,md.). They seem to 
arrange themselves on the strands, connecting the ectodermal 
and endodermal reticulum, and they constitute the mesoblastic 
bands. A series of vacuoles are formed in these bands, around 
which the nuclei arrange themselves in rows, thus giving rise 
to the mesoblastic somites. 
The further development I shall describe in Part 3 of this 
series. ; 
SUMMARY AND GENERAL CoNCLUSIONS. 
The Segmentation is apparently complete, the ovum appearing 
to divide into ectoderm and endoderm cells. 
The so-called endoderm cells are at first without a distinct 
nucleus, they do not get a nucleus until just before the gastrula 
stage. 
All the cells of the ovum, ectodermal as well as endodermal, 
are connected together by a fine protoplasmic reticulum, which 
is placed, as are also the cells, immediately beneath the egg 
membrane, and therefore around a central space. 
Each ectoderm cell consists of a central nucleus around which 
is a close protoplasmic spongework, which, at the outer parts 
of the so-called cell, becomes of a gradually looser nature until 
it runs into the spongework of the surrounding cells. 
Each endoderm mass consists of a central denser spongework 
which gradually becomes looser towards the periphery of the 
mass until it is continued into a fine reticulum. The endoderm 
masses are far apart from each other and are connected by 
this reticulum. 
The continuity of the various cells of the segmenting ovum 
is primary and not secondary, 1. e.in the cleavage the segments 
do not completely separate from one another. But are we 
justified in speaking of cells at allin this case? The fully 
segmented ovum is a syncytium, and there are not 
and have not been at any stage cell limits. I think 
the cleavage should be rather described not as segmentation, 
but a multiplication of the nucleus or centre of force which 
