APLYSIA. 185 



edition (1767) has Laplysia, an obvious misprint for L'Aplysia. 

 In the 10th edition, the animal is called Tethys limacina, but 

 the name Tethys now belongs to a genus of Nudibranchs. 



As a type for dissection Aplysia is of considerable value. 

 Not only is it the largest British Gastropod, but it exhibits 

 intermediate characters between the primitive and more highly 

 specialised forms. Thus, though it has partially acquired a 

 secondary external symmetry, its internal organs are still 

 markedly asymmetrical and afford numerous links in the chain 

 of evidence that detorsion has taken place. The pallio- visceral 

 nerve cords, long but uncrossed, resemble the Streptoneura in 

 the first character and the Euthyneura in the second. There is 

 as yet no indication of the concentration of the nervous system 

 which is so marked a feature of the more specialised Tecti- 

 branchs and Nudibranchs, although other members of the 

 family (e.g., Phyllaplysia, Notarchus) show it. Further, the 

 tendency towards disappearance of the shell and mantle cavity 

 can be understood after a study of this form. 



HISTORY. 



Aplysia has been known from very early times, the first 

 authentic description of it being that of Pliny in the first 

 century a.d. By the ancients it was generally regarded with 

 abhorrence, due, no doubt, to its grotesque appearance and 

 the nauseating odour of the large Mediterranean species. 

 Whatever the' cause, this entirely innocuous creature became 

 invested with poisonous and magical properties, and only one 

 writer of early times (Nicander, c. 150 a.d.) says a good word 

 for it, quoting it as a specific in certain diseases. 



Pliny,* who called it Lepus marmus, the Sea-hare, gives 

 an account of the popular superstitions regarding it. He 



* Pliny describes three species, two in the Mediterranean and one in 

 the Indian Ocean. Of these the last is probably a Dolahella. 



