58 Thomas Henry Huxley 



Huxley's next great piece of work was embodied in a 

 memoir published in the Transactions of the Royal 

 Society in i<S53, and which remains to the present day 

 a model of luminous description and far-reaching ideas. 

 It was a treatise on the structure of the great group of 

 molluscs, and displays in a striking fashion his method 

 of handling anatomical facts, and deducing from them 

 the great underlying principles of construction. The 

 shell-fish with which he dealt specially were those 

 distinguished as cephalous, because, unlike creatures 

 such as the oj^ster and mussel, they had something 

 readih- comparable with the head of vertebrates. He 

 began hy pointing out what problems he hoped to solve. 

 The anatoni}^ of many of the cephalous molluscs was 

 known, but the relation of structures present in one to 

 structures present in another group had not been settled. 



" It is not settled whether the back of a cuttle-fish answers to 

 the dorsal or ventral surface of a gasteropod. It is not decided 

 whether the arms and funnels of the one have or have not their 

 homologues in the other. The dorsal integument of a Doris 

 and the cloak of a whelk are both called ' mantle,' without any 

 evidence to show that they are really homologous. Nor do 

 very much more definite notions seem to have prevailed with 

 regard to the archetypal molluscous form, and the mode in 

 which (if such an archetype exist) it becomes modified in the 

 different secondary types." 



He had taken from the surface of the sea a number of 

 transparent shell-fish, and had been able to study the 

 structure and arrangement of their organs " by simple 

 inspection, without so much as disturbing a single beat 

 of their hearts." From knowledge gained in this 

 fashion, and from ordinary- dissection of a number of 

 common snails, cephalopods, and pteropods, he was 

 able to describe in a very complete way the anatomical 



