STUDIES ON THE DEVELOPMENT OE ECHINOIDEA. 309 
chemical influence exercised by the entering spermatozoon 
on the egg analogous to the action of salts in producing arti- 
ficial parthenogenesis and having no relation to the ordinary 
hereditary action of the spermatozoon. The method employed 
to bring about this anomalous development is to add a small 
quantity of dilute alkali to the water in which the hetero- 
geneous fertilisation is effected. Grodlewski found that the 
addition of 2’5c.c.of solution of NaOH was most effective 
in producing results. I therefore tried the effect of ferti- 
lising the eggs of Echinus with the sperm of Echinocardium 
in vessels of sea-water, to which '5 c.c., TO c.c., T5 c.c., 
2'0 c.c. and 2-5 c.c. respectively of — solution of NaOH had 
been previously added to every 100 c.c. of sea-water employed. 
In the mixture of 2 c.c. of NaOH to 100 c.c. of sea-water 
a few unhealthy granular blastulfe were observed. In none 
of the other mixtures did a single egg develop. 
Now Loeb has shown (13) that it is possible to get the 
eggs of sea urchins to develop if they are treated foi- a very 
brief period with a weak solution of butyric acid, then 
washed in sea-water, and then placed for an hour or so in sea- 
water rendered hypertonic by the addition of a few cubic 
77 < 
centimetres of solution of NaCl to evei-y 100 c.c. of water. 
The effect of the butyric acid is to cause the eggs to form 
membranes closely similar to those formed by eggs when 
normally fertilised. Developmeiit then begins, but if the 
eggs are not subsequently placed in hypertonic sea-watei- 
they break up into sphei’es which I’esolve themselves into 
smaller spheres and the whole egg is thus i-educed to a heap 
of granules. Now if the actual formation of a vitelline 
membrane be carefully watched it will be found that the 
first step in this process is the formation at the surface of 
the egg of a large number of minute spherules whose outer 
walls coalesce to form the membrane. Hence Loeb puts 
