ON THE EXPERIMENTAL HYBRIDIZATION OF ECHINOIDS. 311 



that occasional anomalous oases were found. For instance, in a culture of the cross 

 E. acutus $ X /i'. esculciitus $ , both parents of which are characterized by the 

 absence of the paired tube-feet at metamorphosis, one individual metamorphosed 

 with one tube-foot in each of two of the radii and two tube-feet in each of the 

 remaining three radii. Tliis is shown in Plate 23, fig. !i3. Again, from a certain 

 culture of K. miliaria $ X E- escidentus $ several metamorphosed with four tube-feet 

 in each radius (Plate 23, fig. 95). Finally, one individual in a culture of j^". iniliaris $ 

 X E. acutus $ appeared with one small tube-foot ventral to each of the primaries. 

 All of these Echini appeared to be perfectly healthy. In such cases as these it is 

 impossible to say in what way this character has been inherited. 



These cases are cjuoted to show that very much reliance cannot be placed on the 

 results of the experiments on tlie inheritance of this character. Nevertheless, in 

 the great majority of cases the liybrid urchins completed their metamorphosis in 

 the regular time, and had either the E. esculentus and E. acutus character or the 

 E. railiaris character. 



Crosses between E. esculentus and E. miliaris. 



1. E. esculentus % X E. iniliaris $ — 



In Section 10 it was stated that in 1912, with one exception, all fertilizations of 

 this cross gave larvae with a maternal inheritance of the late larval characters. The 

 Echini which metamorphosed from these cultures had one tube-foot only in each 

 radius, thus inheriting the character from the maternal parent (Plate 23, fig. 94). 



There was one very backward culture, which took over three .months to reach 

 metamorphosis, and then tlie process took place with great difficulty, in the manner 

 described above. Eleven Echini metamorphosed, of which five had the maternal 

 absence of paired tube-feet, tln-ee had the paternal presence of these structures, 

 and three were intermediate, develojiing tube-feet quite irregularly in the different 

 radii. These differences between the individuals of this culture were, however, 

 probably due to ill-health. 



2. E. miliaris ^ X E. esculentus $ — 



The majority of cultures of this cross showed a paternal inheritance of the larval 

 characters in all the plutei. At metamorphosis these cultures gave Echini with a 

 paternal inheritance, that is to say, they had one tube-foot only in each radius. 



The plutei from the cross described in Section 10, some of which inherited the 

 larval characters from the male, others from the female, were divided into two lots 

 before metamorphosis. The maternal larvae did not metamorphose. The paternal 

 larvae gave seven healthy Echini, of which four had three tube-feet in each radius, 

 two had four tube-feet in each radius (Plate 23, fig. 95), and one had one, one, one, 

 two, three tube-feet respectively in the radii. These latter cases seem quite 

 irregular and impossible to interpret in terms of parental influence. If those Echini 



