KOFOID: DEVELOPMENT OF LIMAX. 99 
limite entre les sphérules apparait commo une ligne d'épaisseur trós 
appréciable et dont la transparence contraste avec la teinte foncée des 
cellules; c'est la coupe optique de la couche de sarcode qui règne sur 
toute la surface des sphérules. Mais en outre nous remarquons dans le 
plan de contact des cellules voisines une accumulation de liquide, fait 
déjà constaté par Warneck. Ce liquide va sans doute remplir la cavité 
de fractionnement, mais une partie est aussi expulsée sous forme de 
gouttelettes qui sortent généralment au pôle nutritif. J'ai observé une 
seule goutte chez les Hétéropodes et les Pulmonés aquatiques. . . . La 
"^vitó de segmentation, ou blastocóle, reste presque nulle pendant que 
l'invagination se forme et ne commence à croitre qu'aprés le rétrécisse- 
ment du blastopore." 
The propriety of the use of the term blastocol or segmentation cavity 
to designate the lacunar spaces of the mesenchyma of the gastrula, as 
well as the spaces between the primitive blastomeres, is questionable. 
To be sure the mesenchymatous lacuna are derived from the blastocol 
ather than from an enterocol, in Limax at least ; but our choice of 
terms is not limited to blastocael and enterocol, and it seems preferable 
to apply to those spaces without epithelial lining which lie between the 
ectoderm and entoderm, and are traversed by loose mesenchymatous 
cells and prolongations of the ectoderm cells, a term not already set 
apart for another use. Previous to the formation of these lacuna, all 
the cells of the intermediate layer exist as a solid mass obliterating 
the cleavage cavity. When, however, in Limax the cavity reappears, 
as in Figure 54, it is as a distinct space bounded by germ layers. It 
seems better, therefore, to apply to the spaces mentioned in the seo- 
ond quotation from Fol (p. 116) the same term which is used elsewhere 
for mesenchymatous lacune not lined by a distinct epithelial layer, 
viz. schizocoel. 
Tabl (79, p. 568) notes the presence of a cleavage cavity in the 
twelve-cell stage of Planorbis, and suggests the possibility of its presence 
in the cight-cell stage. It attains its maximum size when the embryo 
consists of twenty-four cells. He mentions the flattening of the blasto- 
sphere which follows this maximum condition, but does not speak of an 
obliteration of the cleavage cavity accompanying it, and considers that 
the cavity is still present at the time the mesoderm cells sink below the 
surface. He makes no suggestion of its recurrent nature at any period 
of its existence. 
3rooks ('80, p. 80) mentions in Physa the “ presence of a lens-shaped 
segmentation cavity, which is enclosed peripherally by the union of the 
