The Embryology of Patella. 
17 
from fifteen to twenty long cilia, which, when the embryo is in 
motion are entirely inactive and either remain straight and motion- 
less or hang gracefnlly to one side in one or more festoons, 
which vary in position as the embryo moves about. When the 
latter is quiet, they are motion less, or at most show only a slight 
restless or uneasy movement. 
At first sight one might attribute to these long cilia the 
function of regulating the direction in which the embryo moves, 
a function, which, considering the fact that the apical plate moves 
first, could be much more easily exercised at the opposite end of the 
embryo. I am inclined rather to attribute the function above men- 
tioned to the smaller cilia around the apical end of the embryo, 
the larger and longer ones being especially modified to serve as 
sensory hairs , a supposition the more reasonable when we con- 
sider their sluggish motion and intimate connection with the very 
early developed rudiments of the sopra-oesophageal ganglion. 
Besides it is not easy to see why the embryo should have two 
rudders of different lengths at the same pole. It is possible that 
the long stiff hairs of the anal cells, which in this stage have 
attained considerable proportions, may assist in guiding the move* 
ment of the embryo, through I have never seen them in motion 
of any kind. 
VI. From the Closure of the Biastopore to the Formation of the 
Nautiloid Shell. 
When the closure of the biastopore has taten pace, the body 
of the embryo has slightly elongated, and the posterior portion 
becomes somewhat flattened dorso-ventrally, which is however 
obscured by the ventrally placed foot which is now rapidly increa- 
sing in prominence. 
The endodei’m which at the end of the preceding section 
had begun to show more regularity in the arrangement of its 
cells, has ceased to fill so completely as before the body cavity, 
and with the rapid division of the cells and their consequent 
reduction in size, has begun to assume the characters which 
distinguish it during this stage. Just after the closure of the 
biastopore, the endoderm cells are very large, their irregularity 
in size and shape still indicating the various modifications be- 
tween the older and more rounded cells and the long wedge* 
Clans, Ai’beiten aus dem Zoologischen Institute etc. Tom. VI, Heft 2. \2 065) 
