president's addkess. 71 



the shell of the parent was functional as a brood-chamber, and that 

 the aptychus, being developed by all individuals, was not confined to 

 the females. 



In concluding this section of my address, let me direct attention 

 to what I believe to be one of the most fruitful outcomes of recent 

 biological inquiry, viz. the wide recognition of the phenomenon of 

 convergence ; and by that I mean the realization, more or less marked, 

 of a similar definitive condition by members of distinct groups of 

 animals — a principle forcibly, though often unconsciously, expressed 

 in the declaration that this or that group is di- or polyphyletic. 



That inextricable tangle the question of mammalian tooth-genesis 

 is to-day yielding overwhelming evidence of its importance ; and it 

 is now a question in the minds of those best competent to judge 

 whether even some of the characters which Man and the apes possess 

 in common may not have been independently evolved, by parallelism of 

 adaptive modification. Among the great vertebrate classes, in the 

 Tunicata, Arthropoda, " Vermes," and away down to animals still 

 lower in the scale, marked indications of the working of this principle 

 are to be recognized. And within the close of the year 1895, under 

 the category of " a special case of mimicry," that which appears to 

 me a convergence has been recognized ^ in the Didymoid Graptolitcs 

 among lowly organisms wholly extinct, by Messrs. Nicholson and Marr. 



So far as I can gather, the evidence for convergence among 

 Mollusca has not been sufiiciently admitted, if indeed it may not have 

 been denied ; but among recent monographs I may cite that of 

 r. Bernard on the hinge-teeth and ligament of the Eulamelli- 

 branchiata, as one which teems with it. The bearings of this 

 principle on our classificatory schemes are only too obvious, and 

 in dealing with it, it cannot be too strongly enforced that its 

 certain appreciation is only possible when systems, and not mere 

 parts, are studied in their natural association. And it is pertinent 

 to this statement that our own members, Messrs. CoUinge and 

 Godwin-Austen, after investigating both the external and visceral 

 anatomy of the slugs of Borneo, have concluded - that these bear 

 the same relationship to the shell-bearing Gastropods of their 

 locality as do similar forms occurring in other regions of the globe. 



Wlien, on a sufiicient knowledge of their all-round anatomical 

 structui'e, we were able to say what it is that constitutes a 

 Cephalopod a Cephalopod, and what a Pteropod a Pteropod, it 

 became only too evident that the development of peri-oral lobes and 

 buccal cones among the latter is but a parallelism with that of the 

 "arms" and suckers of the former. And if, with Kohler, we are 

 to relegate the Sijjhonaria, and with Plate, the Gadinia,^ to the 

 Opisthobranchiata, we have next to consider how far the characters 

 upon which they have so long been associated with the Pulmonata 



1 Nicholson and Marr, Geol. Ma«f. 1895, p. 538. 



- Colliua^e and Godwin-Anstcn, Proc. Zool. Soc. 1895, p. 248. C/. also Godwin- 

 Austen on riiri)i(trio)i, Ann. and Mas,''. Nat. Hist., ser. 6, vol. xvi, p. 4 34. 

 ^ Sitzuugsber. Akad. Wiss. Eeriiu, 1893, p. 962. 



