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



these characters. Such information is obtained by crossing E. miliaris with the 

 other forms. 



The chief distinctions between the larvse of E. esculentus and E. acutus are in the 

 skeletal characters of the early plutei. The inheritance of these skeletal characters in 

 the hybrids has already been described (§ 8). The late larvae of both reciprocal 

 crosses between E. esculentus and E. acutus are shown in Plate 20, figs. 26-43. 

 From these drawings it will be seen that the posterior ciliated epaulettes were 

 developed in the hybrids, as in both parental foi'ms. 



The posterior pedicellariae were present in almost all cases, and were frequently 

 double. 



Crosses hetiveen E. esculentus and E. miliaris. 



1. E. esculentus ^ X E. miliaris $ . (Plate 20, figs. 44-52) — 



The four-armed plutei (Plate 20, figs. 45-48) of this cross showed considerable 

 variation in general shape. The majority inclined to the clear, lightly pigmented 

 type of E. miliaris, but they did not develop the preoral lobe of the latter. Some, 

 on the other hand, were of the E. esculenttis type. In the course of development the 

 aboral pole became more rounded, and, at the time when the anterior ciliated 

 epaulettes were formed, the plutei were either distinctly of the shape of E. esculentus 

 or intermediate between E. esculentus and E. miliaris. 



The body of the fully-formed pluteus (Plate 20, fig. 52) was not so wide as that of 

 E. miliaris, nor so deep and flattened at the aboral pole as that of E. esctdentus. 

 There was a considerable amount of brown pigment, arranged in rather regular 

 patches on the body and also on the arms. The latter were intermediate in form 

 between the stumpiness of E. iniliaris and the length and slenderness of E. esculentus. 

 The anterior ciliated epaulettes eventually surrounded the body, as in the parental 

 forms, and a pair of lateral pedicellariae were developed on the right side of the body. 



The hybrid larvce all inherited the posterior ciliated epaulettes from, the female 

 parent. These structures did not attain the same size as they do in E. esculentus, 

 never completely encircling the end of the body. They were, however, always 

 present (Plate 20, fig. 52). 



In no cases did the hybrids develop any green pigment. They inherited the 

 absence of this character from the female parent. 



In most cases the hybrid plutei inherited a posterior pedicellaria from the female 

 parent, but, as stated above, this character is not invariable in E. esculentus. 



2. E. miliaris % Y. E. esculentus $ . (Plate 21, figs. 53-59) — 



The four-armed plutei (Plate 21, fig. 53) were mostly of the type of £'. miliaris, 

 being pointed aborally and transparent. They were usually rather more pigmented 

 than in E. miliaris. A preoral lobe was developed, but was not so marked as 

 in E. miliaris. A few had the rounded aboral end of E. esculentus. The majority 



