218 M. Ussow’s Zoologico-Embryological Investigations. 
duction of the intestinal tract in Sepiola from two opposite 
invaginations of the upper germ-lamella. 
As regards the body-cavity, I think it will be most correct 
to give this name to the rather narrow and inconsiderable 
space which occurs between the peripheral layer of the dermo- 
muscular layer and one or two rows of the imtestino-fibrous 
layer forming the muscular envelope of the intestinal tract. 
The whole of this completely closed body-cavity is bounded 
by elongated cells of the dermo-muscular layer forming the 
peritoneum or peritoneal sac (in which the alimentary appa- 
ratus, the central organs of the sanguiferous system, and sub- 
sequently also the generative organs are placed). ‘The inner 
nutritive vitellus is never enclosed by a special bounding layer, 
as Kolliker* thinks; but it lies free in the body-cavity, and 
the space occupied by it since the commencement of develop- 
ment represents the segmentation-cavity of the holoplastic 
ova with total segmentation of many other animals. The 
respiratory organs, the two branchie, and the funnel are 
situated in a special open respiratory cavity covered only 
by the ventral part of the mantle, and lined internally with 
simple epithelium forming the continuation of the upper germ- 
lamella, penetrating here during its separation from the ventral 
surface. 
I have still to notice the period of the appearance of the 
nervous system and its mode of formation in the Cephalopoda. 
After a long series of frequently repeated observations relating 
to this question, and always furnishing the same results, I 
have been compelled to give up for ever the hope of finding, 
in the development of the nervous system of the Cephalopoda, 
any resemblance to its development in the Vertebrata, ‘Tuni- 
cata, Annulosa, and Mollusca. Whilst even in many species 
belonging to the types of the Arthropoda and Mollusca some 
ganglia, at least (as has been proved 7), are undoubtedly de- 
veloped from the upper germ-lamella, all the ganglia of the 
Cephalopoda originate from more or less compact thickenings 
of the middle germ-lamella (dermo-muscular layer), and con- 
sequently in accordance with the mode of formation of the peri- 
pheral ganglia in the Vertebrata, which, indeed, has already 
been partially indicated by Metschnikoff { with regard to 
* Loc. cit. pp. 61, 87,167. Metschnikoff has justly rejected this view 
as regards Sepvola. 
+ See the already cited remarkable memoir by Kowaleysky, Mém. de 
VAcad. de St. Pétersb. tome xvi. p. 19, pl. v., and p. 24, pl. vii. ; also 
Bobrezky’s memoir, pl. iii. ; M. Ganin, Warschauer Universitatsberichte, 
1873, i.; and Bericht fiir Anat. und Physiol. 1873, p. 360. 
{ Loe. cit. pp. 41, 67. 
