108 



advanced. Under natural conditions this species will then, evidently, com- 

 plete its metamorphosis in less than two weeks. 



The shape of the larva (PI. IV, Fig. 1) is that typical of Clypeastroid 

 larvae. The arms are rather narrow, of the same width throughout. The 

 vibratile lobes are small, as usual; between the postoral and postero- 

 dorsal arms the vibratile band forms a small, earshaped posterolateral 

 process. There is some red pigment in the point of the arms and in the 

 posterior end of the body. 



The skeleton (Fig. 44) hkewise is of typical Clypeastroid structure, body 

 rod and recurrent rod forming in the posterior end a complicate, fene- 

 strated plate, which is not distinctly thorny. Both the body rod and the 

 recurrent rod may be more or less fenestrated (the thorns along their 

 sides uniting with their ends so as to form holes). The lower ventral trans- 

 verse rod is generally only slightly developed, often forming a small 

 fenestrated plate at its base; sometimes it is not at all developed. The 

 upper ventral transverse rod, on the other hand is well developed. Postoral 

 and posterodorsal rods fenestrated, generally only slightly thorny. The 

 holes in the postoral rod are somewhat unusually large, but diminish 

 in size towards the end of the rod. Anterolateral rod slightly thorny in 

 its outer part. 



Laganum diplopora H. L. Clark, i) 



PI. XIV, Fig. 1. 



On the 7th of July 1914, a few days before I left Japan, I got some 

 specimens of this species, taken at the depth of ca. 800 meters in the 

 Sagami Sea, which were found to contain ripe genital products. Fertili- 

 zation was undertaken and proved to be perfectly successful. The small, 

 very transparent eggs were apparently without a mucilaginous coat; in 

 view of the fact that all other Clypeastroids, the development of which 

 has been studied, have the eggs invested by a mucilaginous coat I would, 

 however, not venture to state definitely that such coat is wanting in this 

 species. It may be so transparent that it has been overlooked (the fertili- 

 zation was undertaken rather late in the evening), or it may have been 

 ruptured by shaking the eggs out of the ovary, as it happened also with 

 Clypeaster japonicus. In the course of three days the embryos had deve- 

 loped into typical young plutei, differing in no way from other young 

 Clypeastroid larvae. It was noticed that the larva all kept swimming 

 close to the bottom of the dish, never rising to the surface of the water, 

 as do otherwise as a rule young Echinoderm larvse. 



^) In the preliminary notice on tlie development of some Japanese Echinoderms (p 547) 

 I designated this species as Laganum fudsiyama. On my return I found it to belong to the 

 closely related species Laganum diplopora H. L. Clark. 



