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Show 664 SIR C. ELIOT ON NUDIBRANCHS [June 19, alimentary tube in Doriopsilla miniata and Doridopsis nigra respectively. It should be remembered, however, that these forms may not be typical in all their details, and that other species may show minor variations. In Doriopsilla miniata the tube which issues from the proboscis describes a curve below the nerve-collar (cf. Vayssi^re, I. c. 1901 : " II [le tube] decrit un cercle complet en avant du collier nerveux, puis traverse celui-ci), and then passes through the collar and above the buccal ganglia which touch the collar to the liver. Its diameter is uniform, and its course behind the collar fairly straight. In Doridopsis nigra the nerve-collar lies immediately behind the proboscis. A straight narrow tube runs through it without making any curves until it has passed through the main body of the nervous system. It then makes two conspicuous bends to the right before entering the liver. In the angle between these two bends the tube is constricted, and here are situated two small salivary glands and the buccal ganglia, which latter are united to the nerve-collar by a pair of connectives which run straight and do not follow the bends of the tube. Behind the buccal ganglia the tube dilates and makes another bend to the right before it enters the liver. It looks as if the arrangement in Doriopsilla miniata were the more primitive. It is much the same as that found in an ordinary Dorid, except that the radula with its pouch and the whole buccal mass have disappeared, leaving in their place a curved suctorial tube. But in Doridopsis nigra this curved tube has been pulled backwards through the nerve-collar, and the buccal ganglia have moved with it, and if, as it is reasonable to suppose, the buccal ganglia mark the commencement of the oesophagus, that organ has very different dimensions in the two genera. Though nothing is known about the food of the Doridopsidae, it is clear that their alimentary organs form an exsertile proboscis and a powerful suctorial apparatus; and perhaps the arrangement found in Doridopsis nigra (which seems to be by far the most usual in the family) allows this apparatus, which probably expands and contracts when taking nutrition, to move more freely. Doridopsis nigra (PI. XLVII. figs. 5 & 7) has not only the two small salivary glands already mentioned, but also a large bilobed gland (PI. XLVII. figs. 5 d <fc 7 d) discharging by a single duct, which enters the wall of the proboscis rather far back, runs forward as a thin tube (PL XLVII. fig. 5 e) in the lower wall of the proboscis, and opens close to the mouth. It is generally known as the ptyaline gland, but, as Hancock suggests, it may supply a secretion which can pierce or benumb the animal's prey. Neither salivary nor ptyaline glands could be found in my specimens of Doriopsilla miniata, and if present at all they must be small. Bergh reports their presence in Doriopsilla areolata and D. pallida, but could not find them in D. Icevis (Siboga, p. 179), which offers many analogies to D. miniata. The large development of the ptyaline gland in Doridopsis would doubtless be |