1911.] 



Studies in Heredity. 



395 



purely maternal characters, and Fischel (2) arrived at the same conclusion on 

 the whole. This conclusion is the more remarkable because Hagedoorn in 

 his experiments used two species of the same genus. Tennent (12) crossed 

 species of the American genera Toxopneustes and Hipponoe and found that 

 the characters of Hipponoe were dominant in the hybrid whichever way the 

 cross was made, but that if the alkalinity of the sea-water were reduced by 

 the addition of dilute acid the influence of Toxopneustes became increased. 

 Lastly Loeb, Eedman King, and Moore in a joint paper published quite 

 recently (9), in which they record the results of experiments with the same 

 two species which Hagedoorn used, arrive at the conclusion that the 

 exhibition of paternal and maternal characters in the hybrid is governed by 

 the principle of Mendelian dominance, since, as they assert, the same 

 characters appear in the hybrid whichever way the cross is made, whether, 

 that is to say, in any particular case the character in question is inherited' 

 from the male or from the female parent. 



During a study of the whole subject which I recently made with the N 

 object of summarising the present state of our knowledge of this question 

 of the inheritance of paternal and maternal characters in the hybrid, I was 

 struck with the necessity of a preliminary thorough investigation of the 

 characters of the normal larvae of the species used in hybridisation experi- 

 ments. The amount of general acquaintance with Echinoderm larvae 

 displayed by several of the investigators who have attacked the subject is, to- 

 say the least, somewhat defective. Thus Herbst (5), who studied chiefly 

 the cross between Sphasrechinus and Strongylocentrotus, attaches great 

 importance to the extent to which lattice-work appears in the skeleton of 

 the arms of the hybrid. In the normal larva of Strongylocentrotus, it is 

 true, all four arms are supported by unbranched calcareous rods, whilst im 

 the normal larva of Sphserecbinus, each of the two posterior arms is 

 supported by parallel rods connected by cross-pieces like the steps of 

 a ladder, an arrangement which is termed "lattice-work." But Herbst 

 fails to take into account the fact that in the normal larva of Strongylo- 

 centrotus a lattice-work skeleton can appear as a variation, and hence an 

 attempt such as he makes to estimate quantitatively the influence of one 

 parent by the amount of lattice-work which appears in the hybrid rests 

 upon an insecure foundation. 



There are, however, two cases known to me where the larvae of two species 

 which can be crossed differ from one another in unmistakable features, about 

 the presence or absence of which there can be no possible doubt. These 

 are, (1) the case of the species Echinus esculents and Echinus miliaris, (2) the 

 case of the species Echinus esculcntus and Echinocarclium cordatum. 



VOL. LXXXIV. — B. 2 G 



