THE EXPERIMENTAL HYBRIDIZATION OF ECHINOIDS. 



131 



EXTERNAL CHARACTERS OF LATE LARVA (FiG. 2). 



The body is not so wide as the pure E. iniliaris, or so deep and 

 flattened at the posterior pole as the pure JE. eseulcntus. There is 

 a good deal of brown pigment arranged in rather regular patches on 

 the body, and also on the arms which are intermediate in form 

 between the stumpiness of pure miliaris, and the length and slender- 

 ness of pure esculent i/s. The deeply pigmented anterior epaulettes 



Fig. 2.- 



-Larva of ^. miliuris i x E. esculentus 9 . Dorsal view, x 36. 36 days old. Tins 

 larva is more advanced than that shown in Pig. 1, and the tube-feet of the 

 the young Echinus are protruded, tu.f. — Tube-feet. The remainder of the 

 lettering as in Fig. 1. 



have nearly surrounded the anterior margin of the body. The posterior 

 •epaulettes are not so far advanced. There are three pedicellariae, one 

 at the posterior pole, and two on the right side, dorsal and ventral, the 

 latter of which does not appear in the figure. On the left side is the 

 young Echinus, well advanced, and with protruding tube-feet. The 

 chief external features of this liybrid are : — 



The anterior epaulettes. 

 The posterior epaulettes. 

 Three pedicellariae. 



One right side dorsal. 



One right side ventral. 



One at posterior pole. 



(c) EARLY DEVELOPMENT OF 



E. MILIARIS $ 

 E. MILIARIS 9 



The four-armed pluteus of U. miliaris is readily distinguished from 

 that of E, esculentus. It is smaller, the posterior end is more pointed. 



