president's address. 223 



appeared by Hacker,^ revealing evidence of structural dissimilarity 

 among the various forms vrhich, by analogy, materially strengthens 

 Verrill's case. The construction of archetypes, and the creation of 

 recesses in our classificatory schemes and museums for the reception 

 of hypothetical ancestral groups, are objectionable practices ; and we, 

 therefore, the more regret the presence in Simroth's volume on the 

 Acephala of the German Plankton Expedition of a supposed ' hypo- 

 thetical primitive mollusc ' — said to have lived between tide-marks 

 in the littoral zone, and to have had a hemi-pelagic larva ! 



Many bushels of apples had fallen to the earth before that which led 

 Newton to consider gravitation, and every milkmaid was aware of the 

 fact which, in Jenner's mind, laid the foundation of the science of pre- 

 ventive medicine. But there are ideas and ' ideas.' In human progress 

 no one does you a greater service than he who demolishes a heresy ; 

 and the real worker in science is he who fairly and squarely records 

 a fact. If he have an idea, let him cherish it; another will ere long 

 intersect it, much to his advantage. 



Among workers in science we now meet with signs of uneasiness 

 concerning the biological outlook ; while in the popular mind tlie 

 notion seems to have arisen that with the historical establishment of 

 the principle of evolution the field is exhausted. To the serious 

 student, however, definitions of classes which sufficed for our 

 immediate predecessors will not suffice in the extended state of our 

 knowledge. The characters common to all living membei's of a 

 group are not those of all that have become extinct. Palaeontology 

 bus shown us that many a structural feature which, from the study 

 of the living alone, we have long regarded as the late outcome of a 

 long series of evolutionary changes, has been anticipated in early 

 geological times ; and we are prone to inquire whether many of our 

 existing groups do not carry us back to an assemblage of ancestors 

 (i.e. may not be polyphyletic) rather than to a single progenitor as 

 is generally assumed. In a word, the field is widening, especially 

 in the department of palaeontology, and its real extent is but now 

 becoming obvious. 



The significance of larval forms among invertebrates has been 

 7uuch under discussion in recent years. No one now dreams of 

 attaching to the ' gastrula ' the far-reaching phylogenetic significance 

 which Ha3ckel claimed for it in 1873. The claims of the jdakula, 

 phuiula, and other early larval differentiations have to be considend.- 

 Concerning the later-foraied types of larvoe, 1 wish especially to 

 point out that while during recent years the idea has grown that the 

 Nauplius may be wholly secondary, Verrill, on behalf of our chosen 

 class of animals, has recently defended^ the earlier notion that 



1 Y. Hacker, Zeit. Wiss. Zool., Bd. Ixii, p. 74 ; auci also Zool. Jahrb. (Anat. 



Abth.), Bd. viii, p. 245. 



2 Cf. E. B. Wilson, Joiiru. Morph., vol. vi, p. 368, aud also J. P. McMurnch, 



Biol. Lect. Wood's IIoll, 189() (Bo.sfou, IStH', p. 79. 



3 A. E. Verrill, Amor. Jouru. Sci., ser. IV, vol. ii, p. 91. 



