49 



NUDIBRANCHIATA. 



NUDIBHANCHIATA. 



to 



Though patient and long-suffering in the c-ndurancs of hunger, they 

 are very voracious. The greater number of them are carnivorous ; 

 living principally upon zoophytes and sponges. The Alcyonium digi- 

 tatum ia a favourite food with the TritQjiiw : and the A ctin ice and 

 Luccnaria: often fall a prey to the attacks of the Eolides. These latter 

 indeed do not scruple occasionally to devour the weaker among their 

 own brethren. 



Most of the species that are found between tide-marks make their 

 appearance periodically, and the common kinds are generally found 

 in considerable numbers for a time, extending from one to three 

 months, after which they almost entirely disappear. This is their 

 breeding season, and it is generally considered that these animals 

 live mostly beyond low-water mark for a great part of the year and 

 come into shallower water to spawn, as is the case with several tribes 

 of marine animals. It is however more probable that the old ones 

 die off before the young are old enough to be observed. It would 

 thus appear that the duration of their existence is but short. 



The following table of the British species, drawn up by Messrs. Alder 

 and Hancock, will supply a list of the British species, and afford at the 

 same time a view of their distribution in depth : 



DISTRIBUTION IN ZONES OF DEPTH. 

 1. Littoral Zone. 2. Coralline Zone. S. Deep- Water or Coral Zone. 



With the imperfect knowledge of foreign species that we yet possess, 



it ia scarcely possible to arrive at any satisfactory conclusion concerning 



the general distribution of the Nudibranchiata in the different regions 



of the globe. So far as the observations of travellers go, they appear 



to be pntty generally diffused throughout all seas and in all climates. 



The tropical forms are, as usual, larger and more brilliantly coloured 



than those of colder climates, but the notices of extra-European 



ipecics are so scanty that we cannot form any idea of their numerical 



preponderance ; nor can wo, for the same reason, point out, as may be 



ni many groups of animals and plants, any particular centres of 



where they are more especially congregated. With the 



mi of a few oceanic wanderers, such as Glaucns and *- 



BAT. HIST. DIV. VOL. IV. 



which have been met with by almost every voyagor, nearly all the 

 Nudibranchs that have been described by naturalists visiting the 

 southern hemisphere belong to the Dorididcs ; and these show a much 

 greater variety of forms than are to be found in the same family with 

 us. It may therefore be inferred that the members of this family are 

 proportionally more numerous in warm climates than in the more 

 northern and colder regions ; but were we to take the number of 

 species at present known as a ratio of their preponderance, we should 

 certainly be very wide of the mark, for it cannot be doubted that a 

 great deal of the apparent deficiency of other genera, in comparison 

 with the DoridUhf, in foreign countries, arises from the want of proper 

 examination, and from the little attention paid by collectors to the 

 less conspicuous forms. It may therefore be expected that when 

 naturalists visiting foreign countries shall have their attention directed 

 more especially to this beautiful race of marine animals, they will not 

 only collect those conspicuous species which, from their size and 

 colour, obtrude themselves upon the eye, but will search out in their 

 bidden retreats the smaller and often more interesting because more 

 varied forms that belong to the other families. 



From the previous table it will be seen that only three families of 

 the Xiulibranchiata are British. The following families are given in 

 Woodward's ' Manual of Mollusca :' 



Doridce, Sea-Lemons. 



Animal oblong ; gills plume-like, placed in a circle in the middle of 

 the back; tentacles two; eye-specks immersed, behind the tentacles, 

 not always visible in the adult; lingual membrane with usually nume- 

 rous lateral teeth ; rachis often edentulous ; stomach simple ; liver 

 compact; skin strengthened with spicula, more or less definitely 

 arranged. 



The genera belonging to this family are Doris, Goniodoris, 

 , Thecacera, Polijccra, Idalia, Ancula, Ceratosoma* 



I'nrii eorillila. 

 a, seen from above ; >>, scf n from below j c, side vle 



Dvrit laccra. 



Doris (Onchi'loris} Ltnctiii. 

 a, side view ; li, seen from be'ow. 



