1893.] Embryology. 291 
same egg membrane. ‘These facts favor the views of Driesch as to the 
equality of the cleavage cells in the echinoderm. Another peculiar 
result sometimes followed the addition of salts, namely, the production 
of twin gastrulse or plutei (without processes) or even of multiple larvæ 
all to be regarded in these cases as due to fusion. The author enter- 
tains no doubt, that by some change in the character of the ectoderm cells 
the larve first adhere and then fuse till there are formed complete twins 
with two separate mouths, ani and (ingomplete) skeletal systems, 
though but a single body space. 
Coming to the main results of the experiments, we find that two 
peculiar larval forms, the potassium larve and the lithium larve may 
be formed instead of the normal larvæ when salts of potassium or of 
lithium are added to sea water. 
The potassium larva is simply a pluteus with its normal digestive 
tract and cilia but without the characteristic pluteus processes or arms 
and: with little or no skeleton. As an example of the amount of 
material necessary to effect this result may be cited one experiment in 
which eggs fertilized in normal sea water were put into 860 ccm. sea- 
water diluted by 140 cm. of 3.7% KNO, solution. The larve lived 
for fourteen days but had scarcely any or no skeleton and no arms. 
The absence of the skeleton is regarded as the chief thing determin- 
ing the absence of the pluteus arms; these, it is believed, naturally 
growing as they are constantly stimulated by the growing skeleton. The 
cells to form the skeleton may be properly arranged, but do not secrete 
the lime salts to form the skeleton. 
This kind of larva may be formed by other salts than those contain - 
ing potassium. The lithium larva, however, is formed only by 
salts containing lithium. 
This latter form may be described as two vesicles attached to one 
another by a hollow stalk. One vesicle has a thicker wall and finer 
cilia on its outside, the other a thin wall and fewer, longer cilia on its 
outside. This larva is actually formed by the elongation of a normal 
blastula followed by a partial abstriction into two vesicular portions. 
It is regarded, however, as having the morphological value of a gas- 
trula which has grown in an evaginated form so that the thicker walled 
vesicle represents the entoderm and the other the ectoderm. 
One experiment taken at random will serve to illustrate the 
amount of salts used; to 1950 ccm. sea-water 50cm. 3.7% LI Cl 
solution were added; the characteristic double vesicle larva were 
formed, but all died on the eighth day. 
