lIuMii llnough nu'tamorphosis, and tlu'ii linllier to rear the 

 metamorphosed hybrids to maturity and I lien again study 

 their offspring. That this can be done is Ijeyond doubt; the way has 

 been shown by Shearer, Morgan and Fuchsi). So far, however, nobody 

 has done this. Ikit, in any case, it shouki be the minimum claim that the 

 investigators should really know the normal sha])e 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 larvfe often not being able to 

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

 that MacBride^) has succeeded in rearing unto metamorjjhosis larvae 

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

 all shows that probably in many ca.ses 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 hvbridization and heredity studies hitherto carried out on Echino- 

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

 a more satisfactory base for the hybridization work in making known 

 the normal larval forms of as many F^chinoderms as possible. — That 

 1 have confined myself to the study of the normal larvye, not entering on 

 hvbridization experiments, does not mean that I take no interest in hybrid- 

 ization studies — on the contrary, I should think such studies, carried out 

 after the ideal sketched above, most fascinating - but' there was simply 

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

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

 been very advantageous in several cases, where material for fertilization 

 was scarce, is in accordance with my wish to study the normal larvae, 

 there being, as yet, not sufficient guarantee that artificially parlheno- 

 genetic larv;e show the normal characters of the larvae to the full extent. 



As already staled il is only a few species oul of the comparatively 

 poor Echinoderm fauna of iMirope and North America which have hitherto 

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

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

 there are still unknown as regards their development. .\nd then the im- 

 mense number of lu-hinoderms peculiar to llie Indo-Pacific region, in- 

 cluding many forms of I lie greatest nu)rphological and systematic import- 



') riu'su auHiors (Op. cit. p. 2.'iti) also point oul tlu' iiiisatisfacloiy charailiT of IIk' usual 

 method, to take only the skeletal slruitures of the first larval stage into consideration in 

 the hybridization studies. 



-) I-:. \V. .Mae Bride. The aretilieial production of Echinoderm larva' with two waler- 

 vaseular systems, and also of larv;e devoid of a water-vaseular system. I'roe. H. Soe. B. 

 Vol. 90. 1918. 



