ANATOMY AND PHYSIOLOGY. 
Moll . 43 
Prior to the segmentation in Loligo pealii , the protoplasm collects at 
one pole, forming a germinal disc, which divides throughout its thickness.. 
It then splits into two layers, ectoderm and mesoderm, the former of 
which alone is present in the future long axis of the embryo, in which 
region also endoderm cells become separated off. Endoderm cells are not 
formed spontaneously from the yolk. The ectoderm and endoderm sur- 
round the whole yolk, while the mesoderm extends only halfway round ; 
Bruce. 
The egg-capsules of Fulgur contain each 12 or 14 eggs, with a quan- 
tity of albuminous material, which appears to be a proteid. Sometimes 
all the eggs develop, but, iu other cases, a large number serve as food 
for the rest. The non-developing eggs neither segment nor disintegrate, 
but are ingested whole by the other embryos. A single polar body is 
formed early and contains yolk-granules. The first two divisions are 
into equal parts, after which four completely protoplasmic micromeres 
are separated off. The macromeres do not divide any further, but new 
micromeres are developed and the gastrula is formed by epibole. The 
formation of the polar body is regarded as dependent upon the relative 
amount of yolk and protoplasm. Segmentation in Platyhelminthes , 
Annelida , Mollusca and Molluscoida seems to be referable to a common 
type. The velum is developed from paired ventral ectodermic folds ; in 
many forms it consists of a preoral band of large cilia, and a postoral 
band of smaller ones. The “ head-kidney ” is absent in Fulgur , but 
present in Paludina and Bithynia ; the secreting cells perhaps originated 
as part of a preoral velar area. The cerebral and pedal ganglia develop 
as usual from thickenings of the ectoderm ; the latter have no connection 
with the byssus gland. The typical apical thickening is found in pul- 
monates but not in Prosobranchiata ; McMuiirich (2). 
In an early developmental stage of Sepia there is below the digestive 
tract a space bounded above by the mesoderm, below by the vitelline 
membrane ; it contains cells derived from the vitelline membrane and 
also free nuclei which do not form cells but result from cells the con- 
tents of which have swollen up and become invisible. Two ccelomic 
cavities pass, one on either side, between the branchial hearts and the 
median arterial heart. Their inner walls afterwards form the pericardium 
and their outer walls the envelope of the branchial hearts ; thickenings 
in the walls of these latter give rise to the pericardiac gland, while the 
generative glands arise on the hinder margin of the ccelomic sacs. 
A comparison is instituted between this and the state of affairs in Cyclas ; 
SCHIMKEWITSCH. 
In the Stylommatophorous Pulmonata the rudiment of generative organs 
may be observed in larvae just before extrusion as a fine cord of cells 
with a distinct lumen, at the side of the right cerebral ganglion ; this, the 
primary duct, elougates, and the hermaphrodite gland appears further 
backward : these are both mesoblastic in origin. The duct and gland 
unite, and the penis is developed as a caecal diverticulum of the former. 
In animals 4-5 mm. long, the vas deferens grows out from the penial 
sac, the primitive duct splits into male and female portions, and the 
outer genital aperture is formed. Primitive ova are also developed in 
