them through metamorphosis, and then further to rear the 

 metamorphosed hybrids to maturity and then again study 

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

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

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

 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 larvae often not being able to 

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

 that MacBride^) has succeeded in rearing unto metamorphosis larvse 

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

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

 than is generally the case. 



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

 the hybridization 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 Echinoderms as possible. — That 

 I have confined myself to the study of the normal larvae, not entering on 

 hybridization 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 partheno- 

 genetic larvae show the normal characters of the larvae to the full extent. 



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

 poor Echinoderm fauna of Europe and North America which have hitherto 

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

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

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

 mense number of Echinoderms peculiar to the Indo-Pacific region, in- 

 cluding many forms of the greatest morphological and systematic import- 



1) These authors (Op. cit. p. 256) also point out the unsatisfactory character ol the usual 

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

 the hybridization studies. 



^) E. W. MacBride. The arctificial production of Echinoderm larvae with two water- 

 vascular systems, and also of larvae devoid of a water-vascular system. Proc. R. Soc. B. 

 Vol. 90. 1918. 



