TERMS USED IN THIS REPORT 31 



mucus glands. They have radial extensions as well of the oral cone, which bears a large number of 

 gonozooids. They possess too, rings of aboral tentacles, and large floats invaginated into the aboral 

 end. They differ widely from Siphonophora, though the two groups, no doubt, had a common 

 ancestor. The Chondrophora are so much more aberrant than the somewhat similar pelagic tubularian 

 Margellopsinae, that they should be treated, perhaps, as a separate order, neither as Hydroida, with 

 which Vogt, Kolliker and Agassiz were inclined to associate them, nor as Siphonophora, as has for 

 long been customary. 



TERMS USED IN THIS REPORT 



I have used the same terms as those used by Bigelow (191 ib) in his 'Albatross' report. A long- 

 stemmed Agalmid is divided into the nectosome above, and the siphosome below. In the early larva or 

 oozooid these two parts occupy opposite sides of the float or pneumatophore. 1 As growth proceeds the 

 growing point of the nectosome, lying as it does just below the pneumatophore, is carried upwards from 

 the level of the growing point or blastocrene of the siphosome, whose oldest gastrozooid (protosiphon) 

 is thus carried downwards. 2 The outer wall of the pneumatophore is called the pnenmatocodon, and the 

 inner wall the pneumatosaccus. Libbie Hyman regards these as the exumbrella and subumbrella 

 respectively of a medusa, a point of view that I hope will be abandoned after reading Garstang (1946) 

 on the subject. The rhythmical contractions of the muscular lining (nectosac) of the nectophores 

 provides jet-propulsion. The nectophores of the Calycophorae include a somatocyst which has 

 vacuolated walls and usually contains a quantity of fat. It is in direct communication with the stem 

 and all the buds (blastozooids) of the original larva (including the protosiphon) or oozooid. The whole 

 forms a floating bud-colony of larval-type polyps or zooids, to which are added precociously the 

 adult-type medusae or nectophores — for swimming only — without manubrium or mouth, and later the 

 gonophores with manubrium but without mouth. At the base of the feeding zooid or gastrozooid is 

 a swollen part, the basigaster, filled with growing nematocysts, from which arises the single tentacle. 

 Its lateral branches or tentilla are provided with complicated nematocyst batteries or cnidosacs. The 

 cnidosac is attached to a pedicel of the tentillum by two structureless, much folded, elastic bands 

 {angle-bands). From this point a broad band (cnidoband) of probably adhesive nematocysts, often 

 spirally coiled, is doubled back towards the pedicel and partially or wholly covered by an involucre. 

 Distad to the attachment of the angle-bands may be a central ampulla and a pair of lateral horns. 

 In the Calycophorae there is usually a distal patch of pear-shaped nematoblasts, and a (sub-terminal) 

 terminal filament bearing numerous nematocysts. Flanking the inner end of the cnidoband of an 

 unexploded cnidosac is a series of large penetrant nematocysts. Upon appropriate stimulation, whose 

 nature, in spite of experiment, is still not understood, the inner end of the cnidoband is flung forward, 

 its outer end anchored to the pedicel by the elastic bands. 



The Calycophorae appear to have lost the aboral end of the larva after the precocious formation of 

 nectophores. They now have no pneumatophore. Their nectophores differ from those of the Physo- 

 nectae in that they include a somatocyst, about the significance of which there has been much specula- 

 tion. Old authors sometimes referred to the other type of nectophore, found in Physonectae, as pure 

 nectophores. 



There is only one other type of zooid commonly called the palpon. In Physonectae it is generally 

 much less developed than the gastrozooid. It does not feed, though its terminal end may occasionally 

 open. Its basigaster is very reduced, and its tentacle or palpacle is simple. 



In the Calycophorae there is no such distinction, or in other words there are no palpons. So that 

 either Physonectae possess reduced or undeveloped zooids (palpons) or in Calycophorae the palpons 

 are upgraded to gastrozooids or else have disappeared. 



1 Text-fig. 3. 2 See frontispiece. 



