STT'DIES ON THE DEVELOPMENT OF ECHINOIDEA. 307 
pipes througli which it is poured into the tanks ; it is only 
necessary to dip up the water from the Firth in an earthen- 
ware or glass vessel in order to provide the larvae with a 
medium in which they can grow and flourish. The eggs of 
both species when shaken out of the ovaries are provided 
with a glassy chorion which makes fertilisation difiicult, but if 
the eggs are allowed to stand in clean sea-water for an hour 
two before being fertilised this membrane disappears. As 
tested by controls in which the eggs of each species were 
fertilised by its own sperm, it was evident that the material 
used was of the healthiest kind. The eggs of Echino- 
cardium fertilised with their own sperm ran through 
their complete larval development and metamor- 
phosed into young urchins in great numbers, 
accomplishing the whole cycle in three weeks. A full account 
of the normal development of this species is reserved for 
another paper. In the case of Echinus esculentus the 
larv'ae lived for three weeks, developed cilated epaulettes and 
all eight arms, but as I had previously given a very full 
accounts of the normal development of this species I gave no 
lurtlier heed to the larvae. My success in rearing tlie 
larvae I attribute to the cultui’es of diatoms provided by 
Dr. biemmill. 
When the eggs of Echinocardium were treated with the 
sperm of Echinus a moderate number of hybrids were pro- 
duced, although possibly not more than one egg in a thousand 
developed. These hybrids lived for eight days, but then, in 
spite of being surrounded by abundance of food, they died. 
When the eggs of Echinus were treated with the sperm of 
Echinocardium about an equal number (one in a thousand) 
developed, and the resulting larvae were of a purely maternal 
type. When, however, the sea-water in which the 
fertilisation was accomplished was previously steri- 
lised by being heated to 70° C. no single Echinus egg 
developed, and when it was found that a certain number of 
Echinus eggs would develop if allowed to stand in clean 
sea-water without the addition of any sperm at all, it became 
