ON THE EXPERIMENTAL HYBRIDIZATION OF ECHINOIDS. 3013 



retained the pointed shape until the development of the anterior ciliated epaulettes, 

 when the aboral pole gi-adually became domed (Plate 21, figs. 54-56). 



The eight-armed pluteus (Plate 21, figs. 57 and 58) had a body not so wide and 

 arms longer than in pure E. miliaris, but the general appearance was similar. The 

 anterior ciliated epaulettes gradually encircled the body. A pair of lateral pedicellariae 

 were developed. 



There ivas never any trace of the iwsterior ciliated epaulettes. The absence of 

 this character was inherited from the female parent. 



Two i^airs of green pigment masses tvere developed at the bases of the anterior 

 ciliated epaulettes. This character, again, was always inherited through the female. 

 When metamorphosis was approaching, green pigment also appeared irregularly in 

 the arms (Plate 21, fig. 59). 



There was never a posterior pedicellaria, but occasionally a group of mesenchyme 

 cells could be observed at the posterior pole of the larva, as if there were an attempt 

 at the formation of the pedicellaria. 



Crosses between E. acutus and E. miliaris. 



1. E. acutus % X E. miliaris $ . (Plate 21, figs. 60-66) — 



The early larvaj of this cross resembled E. acutus rather than E. miliaris in shape, 

 pigmentation, and length and slenderness of the arms. They were distinguished by 

 long oral lobes. 



In general shape the late larvse (Plate 21, figs. 65 and 66) resembled E. acutus, 

 although the arms were not so long as in that S[)ecies. The hybrids all had the 

 materncd posterior ciliated epaulettes, although they were not so much developed as 

 in E. acutus {cf the cross E. escidentus $ X E. miliaris $ ). 



None of the plutei developed green pigment masses. This character, again, was 

 inherited from the mother. 



Some of the larvae developed the posterior pedicellaria, while others lacked it. 



2. E. miliaris % X E. acutus $ . (Plate 21, figs. 67-72) — 



In each culture the majority of the four-armed plutei resembled E. ynilians, having 

 wide and stumpy arms and sparse pigmentation. A few, on the other hand, had the 

 long arms and stippled pigmentation of E. acutus. 



The fully-formed plutei (Plate 21, figs. 71 and 72) resembled E. miliaris in general 

 shape, having wide bodies with domed ends and short arms. They invaHably 

 inhented the complete absence of posterior ciliated epaulettes and the presence of 

 green pigment masses, from the female parent. The posterior pedicellaria was always 

 absent, but, as in the cross E. miliaris '^ X E. esculentus $ , there was occasionally 

 an apical cell-group. 



