228 Scientific Proceedings, Royal Dublin Society. 



present on each arm in the. largest specimen of 15 mm. in length. The 

 maximum length of this species is given by Meisenheimer (1905 a, p. 427) as 

 11-12 mm.; therefore our specimens of 14-15 mm. appear to be the largest 

 yet met with. The central denticle in the median tooth does not seem to 

 appear until the specimen has reached a certain length : thus it was absent in 

 five specimens measuring from I'50-IO mim, and present in three examples 

 of 11-15 mm. In a specimen of 12 mm., in which the central denticle was 

 occasionally distinct, and at other times absent, the left denticle of this 

 tooth was usually missing. The base, even in these large specimens, is not 

 so deep or so well-defined as in Boas' figure (op. cit., fig. 116). The hooks are 

 very variable in length, and in large specimens usually number about forty. 

 Chromatophores were only observed in the largest example, and were 

 restricted to the back of the neck. Schiemenz (op. cit., p. 29) has remarked 

 on the avidity with which the Gymnosomata feed on their relatives the 

 Thecosomata. In the largest of the present specimens the gullet was 

 observed to be of a lovely pink colour. On being opened this was found to be 

 due to the presence of four oblong pink stomach-plates, and a square iridescent 

 one, belonging to some species of the Thecosomata. Two Cladocerans were 

 also present. The fact that these crystalline plates were in the gullet, 

 instead of in the stomach, seems to suggest that such morsels may be too 

 tough for digestion, the adult Gymnosomata having no trace of a masticatory 

 stomach, and that the plates are rejected by the mouth after the animal 

 which owned them has been absorbed, their large size and many angles 

 preventing their passage through the narrow anal tube. Schiemenz (op. cit., 

 p. 30) found Pteropods breeding throughout the winter at Naples, but 

 observed that reproduction occurred chiefly in the spring. He alluded also 

 to the extraordinary forms which these animals sometimes exhibit. In 

 some of the specimens from station S.E. 449 (a May haul), the reproductive 

 organs seem to be so active that in order to make room for the sexual 

 products the proboscis is evaginated to the utmost, and the radula, salivary 

 glands, oesophagus (packed with food), and the liver-stomach can be observed 

 through the transparent wall, all elevated-above the anterior tentacles, and 

 bent over the back, the acetabuliferous appendages being necessarily fully 

 expanded. The penis is evaginated behind the right fin, and the rest of the 

 body presents a normally plump appearance, although, naturally, the 

 diaphragm separating the cephalic and visceral portions, which can usually 

 be clearly seen through the outer integument, is absent. In three other 

 specimens of this haul the digestive organs occupy their usual position, but a 

 portion of the genitalia is placed externally on the right side below the fin. 1 



1 This abnormality is more fully noted under P. paucidens, p. 229. 



