o 



them through metamorphosis, and then further I o rear the 

 metamorphosed hybrids to maturity and then again study 

 their offspring. Thai this can be done is beyond doubl: I lie \\;iy has 

 been shown by Shearer, Morgan and Fuchs 1 )- So far. however, nobody 

 has done this. But, in any case, it should be the minimum claim that tin- 

 investigators should really know the normal shape of the larval species 

 they use for their hybridization studies. It is. of course, more explicable 

 that the students of experimental embryology generally confine their 

 studies to the youngest larval stage, the larva? often not being able to 

 survive after the varied chemical or mechanical treatment. Still, the fact 

 that Ma cB ride 2 ) has succeeded in rearing unto metamorphosis larva- 

 treated so as to have developed a double hydrocoel or no hydrocoel a I 

 all shows that probably in many cases a good deal more might be done 

 than is generally the case. 



Having for a long time fell this unsatisfactory character of most of 

 the hybridi/ation and heredity studies hilherlo carried out on Kchino- 

 derms, one of the objects of my studies was this, to aid in bringing abonl 

 a more satisfactory base for the hybridi/alion work in making known 

 the normal larval forms ol' as many Kchinoderms as possible-. That 

 I have confined myself to I he study of the normal larva-, not entering on 

 hybridization experiments, does not mean that 1 take no interest in hybrid- 

 i/ation studies on the contrary. I should think such studies, carried out 

 after the ideal sketched above, most fascinating - l>nl there was simply 

 no time to extend the researches so far. On the other hand, I he fact that 

 I did not use artificial parthenogenesis either, although that might have 

 been very advantageous in several cases, where material for fcrlili/alion 

 was scarce, is in accordance with my wish to study the normal larva-. 

 there being, as yel, nol sufficient guarantee that artificially parlheno- 

 genetic larva 1 show the normal characters of the larva 1 to the full extent. 



As already staled it is only a few species out of the comparatively 

 pc Echinoderm fauna of Kurope and North America which have hitherto 

 been studied as regards their larval forms. A few of the \\Vsl Indian forms 

 have been studied; but the vast majority of the numerous species occurring 

 there are still unknown as regards their development. And I hen I he im- 

 mense number of Kchinoderms peculiar to Ihe Indo-1'acilic ivgion. in- 

 cluding many forms of the greatest morphological and systematic import- 



') These ;iulll(irs (Op. cil. |). 'J.'ili) also point Ollt till- imsatislaclorx charaeler ol Ihi' usual 

 nu-tlioil, to take only I hi- skeletal structures of the lirsl larval ->ta^i- inln eimsideralion in 

 Ihe hybridization studies. 



2 ) K. YY. MaeBride. The arvlilieial production of Kchinodcrm larva- with t\\o \\aln 

 vascular systems, and also id larva- devoid ol a water-vascular \\ Mem. I'roc. 1'.. Soc. li. 

 Vol. 90. 1918. 



