M. Ussow’s Zoologico-Embryological Investigations. 319 
inversion of the upper lamella. In the former case the upper 
lamella frequently plays the part of a thin external envelope 
to the rudimentary organ, consisting of the dermo-muscular 
or intestino-fibrous layer; or it splits into several layers, the 
lower of which form the organ proper. In the second case 
the upper lamella forms various depressions at different parts 
of the germinal disk, and penetrates into the middle lamella, 
which thus forms the envelope of the organ. 
The following Table furnishes a summary of the mode of 
appearance of each organ :— 
of the upper lamella The eye-ovals. | 
F| = of the dermo- | The mantle, fins, branchiz, 
z g muscular funnel, arms, organ of 
ta eis = layer. taste. 
' oo 2 
= 
lee S 
: = of the intes- , 
an 5 Hing Ehrous The anal tubercle (anal 
Sale cil a sees lobe). 
S| ae ayer. 
Sr 3 | 
3 . 
a of the upper lamella. All cartilages. 
S |S | ofthea 
| 3 = on ae Como Ali central and peripheral 
eet = | muscular seis 
2 S layer. on sat 
ar) ay | 
Bell es 
3 | of the intes- 
ig tino-fibrous | The auricles and ventricles, 
a layer. 
) 
The primitive groove, audi- 
Invagination tory organs, olfactory 
| organs, the anterior and 
or of the upper lamella. posterior parts of the in- 
testinal tract, the ink- 
depression bag, the efferent ducts of 
the salivary glands. | 
As regards the stomach (and also the so-called crop), the 
cecum, and the liver, these are secondary formations, origi- 
nating from dilatations of the original intestinal tube; the 
salivary glands and the so-called branchial hearts must also 
be reckoned secondary organs. 
