282 



MESSRS. C. SHEARER, W. DE MORGAN, AND H. M. FUCHS 



however, is not invariable like the first two, since the posterior pedicellaria sometimes 

 fails to make its appearance in E. esculentus or E. acutvs. 



It will be seen from the foregoing that, with respect to the late larval characters 

 of which the inheritance has been investigated, E. escuhntxcs and E. acutus can be 

 considered as one form. Reciprocal hybrids between them give no information as to 

 the inheritance of these structures. It is from hybrids between E. miliaris and the 

 other two species that the results recorded below have been obtained. 



Below is given a tabular summary of the development of these characters {cf. text- 

 fig. 10, p. 304):— 



24 hours. 



45 „ 

 65 „ 

 4 days. 



10 

 13 



20 



30 



48 



58 



7. Description of Typical Cultures of 1910. 



(1) E. esculentus ^ X E. esculentus S ■ {Cf. Plate 19, figs. 1-9.) 



Blastulse. 



Gastrulfe. 



Active gastrulae. Very light pigment spots. 



4-armed pluteus, with dome-shaped posterior end. 



Plutei rather larger than E. acutus or E. miliaiis. Surface well 



pigmented with fairly regular dots, but no stippling as in E. acutus. 



The apical rods were thin, domed, and spinous. The postero- dorsal 



arms had started and the preoral arms were just visible. 

 Postero- dorsal arms well advanced. 

 8-armed pluteus. Anterior ciliated epaulettes visible. As in all the 



species of Echinus, the pigment dots were more numerous along the 



ciliated bands and at the ends of the arms. 

 The posterior ciliated epaulettes had formed. The jE'cAmits-rudiment and 



one pedicellaria were visible. 

 Most specimens had two lateral and one posterior pedicellarise. 

 One of the plutei had two well-formed A'c/tJftws-rudiments, lying on 



opposite sides of the stomach. 

 Several had metamorphosed and others were doing so. 



(2) E. acutus % X E. acutus J* . {Cf. Plate 19, figs. 10-18.) 

 The development of this culture was considerably slower than that of either 

 E. esculentus % x E. esculentus $ or E. miliaris ^ X E. miliaris ,? , to be described 



