REIGHARD ON THE BIOLOGICAL SCIENCES. 27 



with a series of embryos, we must l<uo\v the vvhoh' structure, not 

 merely a i>art of it. Mono^^raphic vvorlc is here (juite as necessary as 

 in comparative anatomy. 



Many illustrations mij;ht be p;iven of the «;rotes(iue results reached 

 in animal genealoj^y, principally tlii()Ui;h too great reliance on embryol- 

 ogy. That investigators with the same facts before them may reach 

 diametrically opposite conclusions is shown in the attempt to trace 

 the ancestry of the vertebrates. No less than a dozen invertebrate 

 groui)s have been announced from time to time as having furnished the 

 vertebrate ancestor. The ccelenterates, the anelids, the nemertines, the 

 Crustacea, the spiders, Balanoglossus and the tunicates have all been 

 candidates for this honor, and i)erhai>s all deserve it equally. 



>\'ith such results the zoological pendulum may be said to have 

 reached, for the present, the limit of its excursion in the direction of 

 phylogeny. Jt is now beginning to swing in another direction. Within 

 the last five years, zoologists have begun to see that phylogenetic 

 speculations have been to a large extent fruitless of specitic results. 

 They cannot be undertaken to advantage until we have vastly widened 

 our field of knowledge. Then too it is being realized that the con- 

 struction of a phylogeny of aninuils is. after all. not a matter of the 

 greatest consequence. So long as we know that animals are related to 

 one another and so long as we are able to investigate the laws which 

 have governed the establishment of that relationshij), it does not so 

 much matter just irJiaf the precise relationship may be. 



Zoologists are then turning in other directions. There seems to me 

 to be chiefly four: 



1. There is among those engaged in purely descriptive anatomy or 

 embryology a tendency, not yet very pronounced, but yet growing, to 

 return to the monographic method of working. This is a return to the 

 methods of the beginning of the century and betokens a purpose to let 

 speculation rest for a while, until more materials have accumulated 

 upon which to base it. 



2. There is a marked tendency to study variations. The first book 

 on this subject has appeared within a few years, and has stimulated the 

 production of many papers. The purpose of the workers in this field 

 is to determine the nature and range of variation so as to gain a famil- 

 iarity with the nature" of the materials upon which natural selection 

 acts. It may thus be possible, as Bateson points out. for the investi- 

 gator of the future to say not "if such and such a variation should 

 occur,'' but "since such and such a variation does occur." Students of 

 variation hope also to discover some of the laws which determine the 

 production of variations. It is believed that they are not, as Darwin 

 thought, fortuitous, matters of chance, but that they are subject to well 

 defined laws. 



All ])hylogenetic speculation is based upon the idea of homology, 

 but the study of variations has set our ideas of homology toppling and 

 until these ideas are reconstructed we cannot hope for any final 

 determination of animal relationships. 



3. Toward a study of the effect of environment in inducing and 

 modifying developmental processes. Experimental morphology, experi- 

 mental zoology, experimental embryology, are new subdivisions of our 

 subject which expresses this tendency. It is possible to subject de- 



