No. 9.— 1856-8.] CEYLON nudibranchiata, &o. 



81 



that time nothing approaching to a distinct metamorphosis had been 

 known to exist in any of the true Molluscs. 



The Nuchbranchiata exhibit a high state of organization. They are all 

 provided with a powerful muscular buccal apparatus, which has, in some 

 instances, appended to it a gizzard. The oral aperture is guarded by 

 fleshy lips, and the mouth is furnished with a tongue, bearing a spiny 

 prehensile membrane, and occasionally with lateral corneous jaws. 



The oesophagus, stomach, and intestines are well marked ; the former 

 is generally short, and passes from the upper surface of the buccal mass. 

 The stomach is frequently buried in the liver. The intestine is always 

 short. 



The liver presents two great types of form. In the Dondidce and 

 Tritonidce it is entire (excepting in Scyllece, where it is broken up into 

 6 or 7 globular masses), occupying its normal abdominal position ; in the 

 Eolididce it is more or less diffused. 



All the Nudibranchs are hermaphrodites, each individual being fur- 

 nished with male, female, and androgynous parts. These organs, taken 

 together, are very bulky, and occupy the greater portion of the abdominal 

 cavity. They communicate with a common vestibule, opening upon 

 a nipple-like process on the right side of the body, and always below the 

 mantle, when it is present. 



The organs of circulation and respiration consist of central organs of 

 propulsion,— a systematic and portal heart, — arteries, veins, and sinuses 

 or lacunes ; and of laminated, branched, or papillose branchi'ce ; arranged 

 either on the medial line, or along the sides of the back. The flow of 

 blood is rapid ; the pulsations of the heart varying, in the different 

 species, from 50 to 100 in the minute. 



The nervous system presents a high degree of concentration, perhaps 

 higher than in any other group of 3IoIIusca, — and is divided into two 

 very distinct portions : — one, the cephalic or excito-motor ; the second, 

 the splanchnic or sympathetic ; these two portions intercommunicate at 

 several points. 



All the Nudibranchs are provided with auditory capsules. Eyes are 

 also universally present. The dorsal tentacles are the organs of smell, 

 and, judging from their great development, this sense must be more acute 

 in most of the Nudibranchs than it is in any other Mollusc, with the 

 exception perhaps of Nautilus. Touch undoubtedly resides every- 

 where in the skin, but it is specialised in the oral tentacles and parts 

 about the mouth. The lips and channel of the mouth are probably the 

 sent of taste. 



