ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 559 



exists in the Bdelloids and some Rhizota, but has not yet been 

 described in any of the Ploima. The trilobed brain-sac of Gosse is 

 naturally referred by the author to his retro-cerebral organ previously 

 described ; the very much smaller real brain, lying underneath, is not 

 readily seen. 



Echinoderma, 



Development of Ambulacral Appendages in Holothuria floridana.* 



C. L. Edwards has studied the order of appearance of the tentacles, 

 pedicels, and papilla in Holothuria floridana Pourtales, formerly identified 

 as Millleria agassizii Sel. During the fourth day the embryo has a primi- 

 tive symmetry of four tentacles. During the fifth and last day within 

 the vitelline membrane the embryo buds out a fifth tentacle. On the 

 fortieth day a sixth tentacle develops, on the seventy-fifth day the 

 eleventh appears. Their precise positions are noted. The first pedicel 

 has budded from the posterior end of the mid-ventral radial canal on 

 the fourth day ; on the ninth day a second arises ; on the twenty- 

 second day a third appears ; and so on. 



Genus Heliaster.f — H. L. Clark has studied the starfishes of this 

 genus, which are of more than usual interest because of their limited 

 geographical distribution, their exclusively littoral habitat, and the large 

 number of rays which they possess. Seven species are dealt with, in- 

 cluding H. polyhrachius sp. n., with 31-43 rays. The question of the 

 succession of rays in development is discussed. As to systematic posi- 

 tion, it is shown that the relationship with Asterias is very close, the 

 only important differences being in the number of rays, the degree of 

 their coalescence, and the resulting modification of the actual skeleton 

 and arrangement of pedicels. It seems that Heliaster is intermediate 

 between Asterias and Lahidiaster, and, on the whole, it looks as if Lahi- 

 diaster had originated as an offshoot from Heliaster, living in colder and 

 deeper water, while Odinia, and perhaps Brisinga, too, are probably 

 similarly related to Asterias. " Of the factors which have led to the 

 development of the diverse forms of Heliaster, one at least stands out so 

 clearly that there can be little doubt of its importance, and that is 

 isolation." 



Hermaphroditism of Strongylocentrotus.| — G. Gadd records an in- 

 stance of hermaphroditism in Strong ijlocentrotus drcBhachiensis 0. F. Miil., 

 in which there was found to be one male gonad, while the others were 

 female. This condition, it appears, is remarkably rare in Echinodermata. 



Coelentera. 



Minute Structure of Nephthyidse.§ — H. Reinhart has studied 

 Lithophgtum thyrsoides and Dendronephthya maxima, and gives a welcome 

 account of the minute structure. He brings out some interesting minute 

 differences between L. thyrsoides and other species, e.g. as to the mesen- 

 teric filaments. In the gullet of D. maxima there are two kinds of 



* Science, xxv. (1907) pp. 775-6. 



t Bull. Mus. Comp. Zool. Harvard, li. (1907) pp. 25-76 (8 pis.). 



X Zool. Anzeig., xxxi. (1907) p. G35. 



§ Jen. Zeitschr. Naturw., xlii. (1907) pp. 347-74 (1 pi.). 



