20 XUDIBRANCHIATA. 



introductory^ remarks in a condensed form. I liave 

 very little to say in addition. 



" The Nudibrancliiate Mollusca are all marine, and, 

 with the exception of a few species_, are of small size. 

 To some they are known by the familiar name of sea- 

 slugs — a name, however, not exclusively applied to 

 them, as it is given to several other naked mollusks, 

 which, like them, have a resemblance to the land-slugs 

 in the general form of their body. The term, as applied 

 to these animals, is far from complimentary. The 

 land-slugs are generally sombre in colour, and plain 

 and uninviting in form, while these little inhabitants of 

 the deep are often adorned wdth the most brilliant 

 colours, and of forms the most varied and graceful. 

 Their body is usually elongated, soft, and attached 

 through its whole length to the foot or disk upon which 

 they crawl. It is not unfrequently covered with a cloak ; 

 and in the family Dorididce the skin is strengthened 

 with calcareous spicula. The head is anterior, and fre- 

 quently indistinct, bearing one or two pairs of tentacles, 

 the upper pair of which are placed on the cloak when 

 it is present ; and behind them the eyes are situated. 

 But the characteristic peculiarity of these mollusks is 

 the appendages that constitute the breathing- organs. ''■' 

 These last I have described in the systematic characters 

 of the order. 



Omitting anatomical details, I will continue the 

 account of their life-history. 



" The spawn of the Nudibrancliiate Mollusca is de- 

 posited in the shape of a gelatinous band, always ar- 

 ranged in a more or less spiral form, and fastened to 

 corallines and the underside of stones by one of its 

 edges. The ova are minute and very numerous, amount- 

 ing in some species to several thousands. Before the 



