Abstract
(1) Hybridization experiments have been performed in various combinations among 10 different species of echinoids representing 2 orders, 6 families and 10 genera.
(2) It is hard to foretell, merely on the basis of systematic affinity of the materials, whether the cross-fertilization will be possible or not.
(3) The eggs of certain species, for example Temnopleulus toreumaticus, seem to be especially liable to be cross-fertilized by sperms of other species even of remote systematic affinity.
(4) Perfect larvae may be secured in the cross, Temnopleurus toreumaticus egg by Mespilia globulus sperm, and also in its reciprocal cross.
(5) In the cross in which the elimination of some chromosomes occurs in early cleavage stages, the hybrid larvae become abnormal. Even in cases where no elimination of chromosome takes place, abnormal larvae may be obtained.
(6) The genetic affinity of abnormal hybrid larvae can be decided in few cases.
(7) As a general rule, the maternal influence is stronger on the hybrid larvae than the paternal influence.
(8) The same kind of abnormality in the larval skeleton may be brought about either by raising water temperature or by hybridization.
(9) Some hybrid larvae are marked with unusually high pigmentation.
(10) The echinoids may be considered as representing an exceptional group in the facility of cross-fertilization between species even of very remote relationship.
