300 
PKOF. E. AY. YIACBRIUE. 
species of Echiiioidea, and most contradictory results have 
been arrived at, as a sliort review of the principal papers on 
this subject will show. 
Interest in the question of the cliaracter of the hybrid 
larvm produced by crossing two species of Echinoidea was 
first awakened by two remarkable papers of Boveri (1, 2). 
In these papers, which record the same researches, he 
describes tlie effect of fertilising fragments of Sphaerechinus 
eggs with spermatozoa derived from Echinus. He found 
that he obtained some hybrids of purely maternal type, others 
of mixed character, and some very small ones of purely paternal 
type. These last he attributed to the development of non- 
nucleated fragments of eggs which had been entered by 
spermatozoa of Echinus, since he had previously proved that 
non-uucleated fragments of eggs could develop into larvae 
when entered by the spermatozoa of their own species. He 
therefore concluded that the nucleus alone was the bearer of 
heredity, since it could impress an Ec-hinus-character on a 
fragment of a Sphterechinu s egg. 
'I'his conclusion was attacked by Seeliger (17, 18), who con- 
firmed Boveri’s statement that enucleated fragments of eggs 
could be fertilised by sperm of the same species, but who denied 
thatain' hybrids figured by Boveri had been derived from such 
enucleated fragments, since, in a normal hybrid culture, larvte 
of every type occur — from those showing a purely maternal 
character to those which closely approximate to the paternal 
t}qte. Therefore he concluded that Boveri’s inference that 
the nucleus alone was the bearer of the hereditary qualities 
was not sustained by his experiments. Seeliger also pointed 
out that Boveri had not properly described the typical form 
of the larva in each of the parent species, and that no valid 
conclusion as to the character of the hybrid could be drawn 
until this had been done. 
Hriesch (5) then took up the subject, and pointed out that 
in crosses of Sph terechinus and S tr o n gy 1 o cen t r o t us 
Echinus the hybrids could be of purely maternal type in 
respect of (a) rapidity of development, (b) number of uiesen- 
