546 CKESSAVELL SHEARER AND DO ROTH V JORDAN LLOYD. 
While tlie long slender arms of the partlienogenetic larvae 
is the most obvious feature by whicb in the early stages they 
can be distinguished from the normal ones, a constant 
difference is also present in tlie arrangement of the pigment. 
In the normal larvae this is more or less sharply localised in the 
tips of the arms, and in definite regions of the body, where 
it collects in dense masses. In tlie parthenogenetic larva 
this arrangement is much less definite, and the pigment 
seems more uniformly distributed throughout the arms and 
body. Again, all our parthenogenetic larvae have shown a 
slight opacity of their cytoplasm, no matter by what methods 
they have been obtained. In the normal larvm the cytoplasm is 
extremely clear and transparent, while in the parthenogenetic 
larvae it never attains this excessively transparent condition. 
Beyond these differences just enumerated, there seems no 
distinction between the parthenogenetic larvae and the normal 
ones, and these differences, after all, are of minor importance. 
We have always been able to distinguish one from, the other, 
however, throughout the course of our work. 
Summary. 
This work was carried out during the seasons 1911 and 1912 
at the laboratory of the Marine Biological Association, 
Plymouth. The experiments were made in order to obtain a 
method that could be applied to the sea-urchins of the 
English coast, and in the hope of raising some of the partheno- 
genetic larvm to maturity. 
We have been successful in rearing the plutei through 
the late stages, and large numbers in our cultures formed 
Echinus-rudiments. A few of the larvae completed their 
metamorphosis, but we have not succeeded in getting the 
young urchins to live for more than a few weeks. In all 
about fifteen plutei underwent metatnorphosis. 
The methods used were those elaborated by Loeb and by 
Uelage, and a new method which combined certain features 
from each of these. 
