ARTIFICIAL PARTHEIS^OGENESIS IN ECHINUS ESCULENTUS. 527 
pluteus skin^ but in nearly all cases the young Echinus fails 
in the end to absorb this completely, and remains indefinitly 
in this condition till it dies. 
As the mouth and anus of the young' sea-urchin do not 
appear till about the end of the first week after metamorphosis, 
the inability of the larvte to get rid of the remnants of the 
pluteus so unduly lengthens the process of metamorphosis, 
that they seem unable to live the length of time required 
afterwards, until the mouth and anus form, aud they are able 
to take food. This would seem to be the explanation of the 
almost invariable death of the larvae during metamorphosis. 
As we have said, large numbers of our parthenogenetic plutei 
reached this stage, and then apparently died of starvation, 
AVe have been unable to get them to metamorphose more 
cptickly, although several changes of food were tried in the 
earlier stages, in the hope that this might give better results. 
If the larval rate of growth could be accelerated slightly at 
this point, in metamorphosis, parthenogenetic young Echini 
could be obtained probably as readily as the normally fertilised 
ones. 
In the use of sea-water in all our experiments we have 
observed certain ]3recautions to prevent any possible infection 
by sperm. From experiment Ave have found that in no case 
do the sperm of Echinus at Plymouth survive or remain 
alive after standing for more than thirty-six hours. We have 
used Avater collected in large sterilised carboys (3-4 gallons 
capacity) from some seven miles out from the Plymouth break- 
Avater and then brought into the laboratory and alloAved to 
stand for a week or more before being used. We liave never 
had any of our controls go Avroug from the use of this Avater, 
and therefore Ave have concluded that any possible infection 
from it has been avoided. AVater collected in this AA'ay and 
alloAved to stand in the above-described manner, Ave call 
outside Avater.” This outside water never seems to 
contain any plutei as apparently did the water used by 
Delage (5), so we have not resorted to filtering it to prevent 
any contamination from this source. 
