Archetypal Mollusc 59 



structure of cephalous molluscs. The next natural 

 step, he stated, would have been to describe the em- 

 bryonic development of the organs of these different 

 creatures in order that a true knowledge might be 

 gained of what were the homologous or really corre- 

 sponding parts in each. Having had no opportunity 

 to make such embryological studies for himself, he fell 

 back on numerous accounts of development by Kol- 

 liker, Van Beneden, Gegenbauer, and others, and so 

 gradually arrived at a conception of what he called the 

 " archetype " of the cephalous molluscs. As the word 

 archetype was borrowed from old metaphysical ideas dat- 

 ing back to the time of Plato, he took care to state that 

 what he meant by it was no more than a form embody- 

 ing all that could be affirmed equally respecting every 

 single kind of cephalous mollusc, and by no means an 

 " idea " upon which it could be supposed that animal 

 forms had been modelled. He described this archetype, 

 and showed the condition of the different systems of 

 organs which it could be supposed to possess, and how 

 these organs were modified in the different existing 

 groups. This archetypal mollusc of Huxley's was a 

 creature wnth a bilaterally symmetrical head and body. 

 On the ventral side of the body it possessed a peculiar 

 locomotor appendage, the so-called foot, and the dorsal 

 surface of the body secreted a shell. Its nervous system 

 consisted of three pairs of ganglia or brains, one pair in 

 the head, one in the foot, and a third in the viscera. 

 He shewed how the widely different groups of cephal- 

 ous molluscs could be conceived as modifications of 

 this structure, and extended the conception so as to 

 cover all other molluscs. 



Quite apart from the anatomical value of this paper, 

 and although all technical details have been omitted 



