432 



SCIENCE 



[Vol. LV, No. 1425 



the last week in March or early in April, were 

 carried from Tobago to Copenhagen via New 

 York, arriving in Denmark, June 1, still living, 

 though not thriving! Besides the larviE whose 

 parentage was certain, Mortensen describes and 

 discusses the relationships of nine eehinoid 

 larval foi'ms taken in tow nets. 



Among the sea-stare, artificial fertilization 

 was successful with eleven species, and the 

 larvse resulting are described in ten of them, 

 to a greater or less extent. Owing to unsatis- 

 factory preservation no asteroid larvte from 

 tow-net collections are described. With the 

 holothurians and ophiurans, particularly the 

 latter, artificial fertilization is exceedingly diffi- 

 cult to obtain and with only two species of 

 brittle-star (both at Tobago) was Mortensen 

 able to study material derived from eggs fer- 

 tilized in the laboratory. With holothurians, 

 artificial fertilization was successful in three 

 species, but with two of these the larvas only 

 lived two or three days. On the other hand, 

 Mortensen describes three forms of a note- 

 worthy Auricularia, one from Tobago, one 

 from Misaki, and the third from New Zealand 

 waters, and no fewer than 35 ophiuran lai-vse, 

 whose parentage is unknown. The most extra- 

 ordinary fact recorded in this section is that 

 certain Ophioplutei do not end their free- 

 swimming existence by complete metamorphosis 

 into miniature brittle-stars, but rather give off 

 the new ophiuran as a sort of bud, and then 

 apparently regenerate a new larval body in 

 jilace of the original one. If this new body is 

 capable of giving rise to a new ophiuran by a 

 second metamorphosis, we have here, as Mor- 

 tensen says, the only case of metagenesis known 

 in the whole Echinoderm phylum. But the evi- 

 dence is tantalizingly incomplete. 



The last fourth of the volume, entitled 

 "General Part," is divided into three sections, 

 a short one on "Classification," a longer called 

 "Morphology, Phylogeny, Biology," and a few 

 pages on "Geographical Distribution." In the 

 first section, Mortensen raises the question 

 whether there is any correspondence between 

 groups of larv» arranged according to struc- 

 ture and the natui-al groups of the adults, and 

 so far as the major groups of echini are con- 

 cerned, he answers the question in the affinna- 



tive with little hesitation. He has further 

 unquestionably demonstrated that no classifica- 

 tion of echini can henceforth be accepted which 

 does not give fair consideration to the charac- 

 ters of the larvae so far as they are known. 

 As for the ophiurans on the other hand, we are 

 on much less sure ground, nor can we make 

 very practical use of the ophioplutei in classi- 

 fication until a far larger number of them have 

 been traced back to their parent forms. Among 

 the Asteroidea, too, we still lack sufficient 

 data, in spite of Mortensen's masterly efforts, 

 but enough facts are known to warrant the 

 hope that the various larval forms will prove 

 of great value in tracing relationships within 

 the class. The Crinoidea and Holothurioidea 

 are still largely terra ineognita, so far as larval 

 forms are concerned. In the pages dealing 

 with the morphology of the larvoe, a number 

 of debatable points are discussed and one very 

 important one is emphasized, namely, that 

 there is no homology between the sueking-disk 

 of a brachiolarian larva and the Pelmatozoan 

 stalk.- The remarkable animal described by 

 Koehler and Vaney as Stellosphcera mirdbilis 

 is shown to be a larval form of a sea-star, 

 probably Pedicellaster sexradiatus. After a 

 detailed discussion of the various larval forms, 

 Mortensen pays his respects to Grave's theory 

 that the primitive echinoderm larval form had 

 transverse rings of cilia, and then passes on to 

 an interesting discussion of the proposals of 

 Boas, Simroth and A. H. Clark regarding the 

 phylogeny of the echinoderms, though the ideas 

 of the last two are dismissed briefly, their refu- 

 tation being designated "a superfluous task"! 

 There then follow discussions of Giard's theory 

 of poicilogony, as applied to echinoderms, of 

 the rate of growth of larvae, and of the relation 

 of temperatiu'e to the production of matured 

 reproductive cells. The pages devoted to geo- 

 graphical distribution deal mainly with the 

 matter of the influence of currents in the dis- 

 tribution of echinoderm larviB and the probable 

 existence of vertical upward currents, which 

 are important in bringing the larvae of deep 

 sea forms to the surface. 



The volume closes with a brief appendix and 

 a very full explanation of the admirable 

 plates. There is no bibliography and no index. 



