XVI ECHINODEEMATA 523 



These fall into two categories : (1) Experiments on fertilization ; (2) 

 Experiments with the developing embryo and larva. 



1. Seeliger (1894) has proved that if an egg be broken into 

 two parts, one of which possesses the nucleus and one of which 

 does not, both fragments can be fertilized, and both will develop 

 into apparently normal larvae. Loeb (1910) has proved that if the 

 alkalinity of the sea -water be slightly increased by the addition 



of from 1 to 2 per cent of t^ NaHO, it is possible to fertilize the 



eggs of some species of Echinoidea with the sperm of Asteroidea, 

 Ophiuroidea, and Crinoidea. Godlewski (1906) has even fertilized 

 the enucleated fragments of Echinoid eggs with Crinoid sperm, and 

 has obtained gastrulae. Finally, Kupelwieser (1909) and Loeb have 

 succeeded in fertilizing Echinoid eggs with the sperm of MoUusca 

 (Chlorostoma and Mytilus), and in obtaining larvae which resemble 

 closely the normal four-armed Echinopluteus. 



In some cases, as Kupelwieser 'has shown (1909), the chromosomes 

 of the spermatozoon do not enter the first spindle of division which is 

 formed in the egg ; so that the action of the spermatozoon must be 

 regarded as stimulating the egg to parthenogenetic development, but 

 not as conveying its own hereditary qualities; and in these cases 

 the resulting larvae show purely maternal characters. But this may 

 be the case even where a genuine fertilization appears to take place, 

 and the chromosomes of the spermatozoon enter the first spindle, as 

 Godlewski showed is the case when the uninjured eggs of Echinoidea 

 are fertilized with Crinoid sperm. 



Still more startling is it to find that this may also be the case, as 

 Shearer, Fuchs, and De Morgan (1912) have shown, with the hybrids 

 of UcMnus esculentus and M miliaris, two species which are easily 

 crossed. Whichever way the hybrid is made it may exhibit purely 

 maternal characters, and these hybrids have been reared through 

 the metamorphosis. These authors have also shown that the 

 character of the hybrid obtained by fertilizing the eggs of Echinus 

 miliaris with the sperm of Echinus esculentus, varies from year to 

 year ; in . one year it was purely maternal in character, in the next 

 of a type intermediate in character between the larvae of the two 

 parent species. Even the hybrid obtained by crossing forms belonging 

 to different orders of Echinoidea is not always maternal in character, 

 as we ourselves showed by crossing Echinus esculentus and Echino- 

 cardium cordatum. The hybrids between these two species only live 

 eight days, nevertheless, although the two parents are very widely 

 separated in systematic position, the hybrids show unmistakable 

 paternal features as well as maternal ones. 



The question now arises whether, if parthenogenetic development 

 can be initiated in the eggs of Echinoidea by substances contained in 

 the sperm of MoUusca, which do not convey any hereditary qualities, 

 it could not also be initiated by dead solutions of an organic 

 or inorganic character. This question has been answered in the 



