34 DISCOVERY REPORTS 



Seven specimens were taken at the surface at 'Mabahiss' Stations 39 (see Chart, p. 10) and 99. 

 It was on Indian Ocean material that Linnaeus based his Medusa porpita, to which the present 

 material probably belongs. So far, a critical comparison of Indian Ocean, with Atlantic or Pacific 

 material appears not to have been made, although Bigelow (1904) described and figured some 

 from the Maldive Islands. Leloup (1934ft) identified some taken off the Madras coast, stating that 

 this species is common in the Indian Ocean, but without giving further details. I am unable, 

 without good material of all growth stages from all three oceans, to make the desired critical com- 

 parison. Examination of such material and critical descriptions as are available, leads me to suspect 

 that one species only is to be found in all three oceans. If so, it should bear the name porpita 

 (Linne.) 



A few counts of the stalked tentacular nematocyst clusters of the long rows gave the figure 21-24, 

 and of the short rows 10-13. The numerous tubercles are obvious and have no connexion with the 

 stigmata which are few and become covered not far from the inner edge of the limbus. The radial 

 plications of the surface of the disc are slight. The limbus is comparatively narrow as in Porpita pacifica. 

 In a specimen ('Mabahiss', 23. xii. 33, near St. 99) 3-9 cm. in diameter, the limbus measured 3 mm. 

 In another 2-7 cm. in diameter, it measured 2 mm. The canals of the limbus are irregularly arranged 

 and not radial. In all these respects the Indian Ocean and Pacific forms agree. 



Velella velella (Linne), 1758. 



Velella spirans Forskal, 1775; Chun, 18976. 



The development of the Conaria-larva, first described by Woltereck (1904, 1905) was interpreted 

 by Leloup (1929) and Garstang (1946); and the further development of the Rataria- or Ratarula- 

 post-larval stages are now fairly well known. Likewise the young medusae {Discomitra Haeckel, 

 1888 ft, p. 39, pi. 50, fig. 8) from the time when they arise as buds on the walls of the gonozooids 

 to the time when they are shed, are well known. They are of the Tubulariid type, the tentacles, 

 usually undeveloped, bearing four radial canals and four radial, exumbrellar rows of nematocysts. 

 In the youngest stages these rows extend only half-way to the apex, but later reach all the way up. 

 Such Discomitra medusae may be compared with the well-known Tubulariid medusae, Hybocodon 

 prolifer and Ectopleura dumortieri, the earliest stage of the latter having only one tentacle, three and 

 four being developed later on. The possession by Velella and Porpita of this type of medusa appears 

 to confirm Garstang's view about the Tubulariid ancestry of the Disconanthae (Chondrophora). 



Not so well known as Rataria and Discomitra is an apparently quite different type of medusa 

 Chrysomitra striata (Gegenbaur), the genus founded by him in 1857 for a little free-swimming medusa 

 Phorcynia striata (not stricta) described by Kolliker (1853 a) with from thirteen to sixteen radial canals 

 and one or two tentacles. This Chrysomitra medusa (not larva) is commonly said by writers of text- 

 books to come from Velella, but I am not yet satisfied that this has been proved. It possesses exum- 

 brellar nematocyst tracts, but in appearance differs from Discomitra. Its direct connexion with Velella 

 was not observed by Gegenbaur, but on account of the nematocyst tracts and the ' yellow-cells ' in the 

 sub-umbrella in both forms, and the appearance of rudiments of further radial canals growing out 

 from the stomach in some specimens of Discomitra, Gegenbaur thought it reasonable to assume their 

 identity. That this is very probable has been shown by the micro-photograph by Ankel (195 1) of living 

 specimens of Discomitra recently freed by Velella. One of the medusae has a single small tentacle of 

 the Chrysomitra type, but the rest of the medusae are in the Discomitra stage. Metchnikoff (1886) 

 recorded that on two occasions in January and February 1883, he fished at Messina some sexually 

 mature medusae of Velella and he gave good figures of the single amoeboid egg, the four testes, the 

 sperm and the medusa itself. The medusa had only four radial canals and a single tentacle. He likened 



