Ceylon Nndihranchiate Molluscs, and Zoophytes. 89 



extrusion from the egg a very different form and character from those 

 which they are afterwards destined to assume. In this first stage of their 

 existence, they have the appearance of small animalcules, swimming freely 

 through the water by means of two ciliated lobes, and have their body 

 covered by a nautiloid shell furnished with an operculum. Up to that 

 time nothing approaching to a distinct metamorphosis had been known to 

 exist in any of the true Molluscs. 



The Nudibranchiata 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 Dorididse and 

 Tritonidse it is entire (excepting in Seylleas, where it is broken up into 

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

 Eolididse it is more or less diffused. 



All the jSTudibranchs 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 abdo- 

 minal 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 branchiae ; 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 Mollusca, — and is divided into two 

 very distinct portions ; — one, the cephalic or ex cito- motor ; the second, 

 the splanchnic or sympathetic ; these two portions intercommunicate at 

 several points. 



All the Nudibranehs 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 ex- 

 ception perhaps of Nautilus, Touch undoubtedly resides everywhere in 

 the skin, but is specialised in the oral tentacles and parts about the mouth. 

 The lips and channel of the mouth are probably the seat of taste. 



1858.] 



