ARTIFICIAL PARTHENOGENESIS IN ECHINUS ESCULENTUS. 525 
with sperm. This clearly shows that the growth of the 
parthenogenetic plutei to the sexually mature stage is well 
within the range of possibility if sufficient time and care be 
taken Avith them. 
Delage (5) has been the only investigator Avho has 
attempted to raise parthenogenetic plutei to a late stage. 
He obtained in all some six completely metamorphosed 
urchins of Strongylocentrotus lividus. Two of these 
attained considerable size, and one finally developed rudi- 
mentary gonad cells. Three of these six were obtained by 
his HCl and ammonia method, and three were derived from 
his tannin and ammonia method. 
With the exception of this work of Delage (5), no attempt 
has been made to rear parthenogenetic plutei, and their 
characters have not been closely compared with those of the 
normal larvae. In our work tve have carefully compared the 
growth of the two at different ages, from the blastula to the 
metamorphosed Echinus stage. This comparison has clearly 
established the fact, that there is always a slight difference; 
and that once the features that characterise both are known, 
it is never possible to mistake one for the other. That there 
should be a slight difference between the two is not unlooked 
for, when we consider that it has now been established that 
the parthenogenetic larvas, in the early stages at least, 
develop only in the presence of the reduced number of 
chromosomes. (Hiudle [6] and Wilson [21].) 
These differences are most marked in the length and shape 
of the arms and in the pigmentation. In the later stages 
(eight-armed pluteus) the parthenogenetic are always dis- 
tinguishable from the normal larvae, by a slight granular 
condition of the protoplasm. The relative rates of growth 
differ greatly, development of the parthenogenetic larvae 
being much more rapid in the early stages up to the four- and 
eight-armed pluteus, Avhile after this it is much slower than 
in the normally fertilised ones. While the normal larvae 
nsually metamorphose in five to six weeks frbm the time of 
fertilisation, none of our parthenogenetic larvae have meta- 
