THE DEVELOPMENT OF ECHINOIDS. 337 



forehead, as it may be called, long remains a feature of the E. 

 miliaris larvae ; it is seen as a lip overhanging the mouth in 

 plutei with four processes completely developed (see fig. 1, //*.). 



In addition to this feature the four-armed pluteus of E. 

 miliaris is distinguished from that of E. esculent us by its 

 more pointed posterior portion, and by the smaller length of 

 the processes in comparison to the body (comp. figs. 2 and 3). 



In later stages the posterior pole of the E. miliaris becomes 

 rounded, but then the pluteus is broader in proportion to its 

 depth than is the case with E. esculentus, approximating 

 more to the shape of an Ophiurid pluteus, or ophiopluteus, as 

 Mortensen terms it. 



The ciliated epaulettes develop about the middle of the third 

 week of larval life. A new distinctive feature is now added to 

 those already possessed by E. miliaris. Just anterior to each 

 epaulette there is a large mass of bright green pigment. The 

 epaulettes ofE. esculentus are, on the other hand {pig.,f[g. 4), 

 loaded with reddish-yellow pigment. 



So far as I could observe, the four primary epaulettes at no 

 time form part of the general ciliated band, but are of inde- 

 pendent origin. In the pluteus of Echinus esculentus, 

 in addition to these, however, in the fourth week two posterior 

 ciliated epaulettes are formed, one on each side by abstriction 

 from the ciliated band just where it bends from the postero- 

 dorsal to the post-oral process (Mortensen's notation). I did 

 not succeed in bringing the larvae of E. miliaris quite as far. 

 These posterior epaulettes are mentioned for the first time in 

 Mortensen's work cited above ; they are there described in two 

 undetermined forms of larvse. The drawings are very poor, 

 and it is not possible to be sure whether these larvae are 

 identical with one or other of the forms I have described, but 

 it is worthy of notice that E. esculentus is placed by Mor- 

 tensen amongst forms distinguished by not possessing these 

 epaulettes. It is therefore quite possible that here, again, the 

 old error has been made of mistaking two stages in the same 

 life-history for two different species. 



The oldest stage ofE. esculentus which I succeeded in rear- 



