77 



tion in the middle above the stomach. The digestive organs show the un- 

 iisual feature of a small intestinum, well separated from the rectum by a 

 constriction. The pigmentation consists of scattered, red grains; there are 

 no distinct pigment spots in the arm points. 



Regarding the skeleton I can only quote from my notebook, that it 

 is very robust, forming a basket structure, "somewhat extra complicate" 

 and strongly thorny. (This probably means that the recurrent rod is 

 double as in other Echinometrids). The postoral rods are fenestrated, 

 the anterolateral rods somewhat stronger than usual. In one of I he oldest 

 specimens the posterodorsal rods had begun lo form, so that it could be 

 ascertained that also these rods are fenestrated. - That the fully formed 

 larva will prove to have a posterior transverse rod there is not I he slightest 

 reason to doubt, but none of the larvae developed far enough lo show il. 



It is quite a problem to understand how the young metamorphosing 

 Echinoid can succeed in attaching itself to the rocks, without being washed 

 off or otherwise crushed by the surf. Also the development of the peculiar 

 spines, so well adopted to its unique habits 1 ), would be exceedingly 

 interesting to follow. 



Heterocentrotus mamillatus (Klein.) 



Fertilization of this species, which was found here and there under 

 stones and coral blocks in the rock ponds near Hilo, Hawaii, was under- 

 taken on the 8th of April. The culture was not very successful, bul some 

 specimens developed normally and reached the first Pluteus stage, bul not 

 beyond that stage. For want of sufficient material no new culture could 

 be started. The skeleton of the preserved specimens of the larva having 

 been dissolved, no information can be given beyond the observations from 

 the living specimens stated in my notebook. 



About the first developmental processes it is only noticed thai the em- 

 bryos were in the gastrula stage 24 hours after fertilization; lliey were 

 rather opaque. The young Pluteus is only slightly pigmenlaled. some 

 scattered red grains are found in the body, nothing in the point of the 

 arms. Judging from the preserved specimens the shape of Hie young 

 Pluleus appears to be much like that of Clolobocentrolus. The body skelelou 

 forms a complicate basket structure. The posloral rods are feneslraled. 



The statement that the basket structure of the body skeleton is com- 

 plicate" makes it highly probable that also this species has a double 

 recurrent rod like the other Echinometrids. 



') The same habit of living on rocks exposed to I he surl was most probably adopted by 

 the extinct Heniicidarid, Acrocidaris nobilis Ag. as also by the peculiar extinct Asteroid. 

 Sphxraster. 



