STUDIES OX THE DEVELOPMENT OF ECHINOIDEA. 303 
with the result of fertilising the eggs of Sphserechinns with 
the sperm of Strongyloceu t rotu s and of Ecli in us, arrives 
at much the same results as Doncaster, hut he admits that 
there is also a factor independent of temjrerature which 
determines the greater or less predominance of paternal char- 
acters, and this he finds in the varying character of the eggs. 
In a subsequent paper (11) he records the i-esults of the experi- 
ment of initiating parthenogenesis in the eggs of Sphrn- 
rechinus by treating them for a short period with valerianic 
acid and then fertilising them with the sperm of Strongylo- 
centrotus. Under these circumstances he claims that he 
obtained a displacement of the development in the maternal 
direction, and he maintains that in a few cases he even obtained 
a larva maternal on the one side of the body and paternal on 
the other — a circumstance which he accounts for by supposing 
that the spermatozoon had entered the egg after the egg- 
nucleus had divided and had united with one of the two 
daughter-nuclei so formed. 
Fischel (7) a little later dealt with the Ipybrids produced 
by crossing Arbacia and 8 ph rnr e ch i n u s and also 
Arb acia and Strongylocentrotus. (It is to be noted 
that he persistently and erroneously uses the term Echinus 
brevispinosus for S ph aer e ch i n u s gr an laris). He 
arrived at results of generally the same character as those 
gained by Driesch : but he tries to show that the effect of 
foreign sperm entering the egg is to interfere with the normal 
distribution of pigment in the egg. He asserts that the 
spermatozoon can influence the rapidity of development, the 
form and size of the larva, the development of pigment, the 
skeleton and the histology of the cells. 
Tennent (22) tried the experiment of crossing the American 
forms Toxopneustes and Hipponoe. The larvae of Toxop- 
neustes are like those of Strongylocentrotus. Those of 
Hipponoe, on the contrary, resemble those of Sphaerechinus. 
'I'he cross could be made by using Hipponoe as male or as 
fejuale parent, but in either case the larvae showed the influence 
of Hipponoe as evidenced by the “lattice-work” in theskeleton 
