44 DISCOVERY REPORTS 



Arrangements [i] and [5] are at first sight incompatible. Further study of available pickled material 

 should clear up this point, though it could be done best in the field where musculature can be relaxed. 

 A study of old figures and diagrams will not help much. Haeckel's figures of larvae are not reliable. 

 He would have us believe, for instance, that the pneumatophore arises as the basal part of the bracteal 

 canal. 



Physophora is an interesting animal to study alive: it is very active and responds readily to stimuli. 

 If the air-sac is touched when the animal is at rest all the palpons are at once thrown up. Even a larva 

 can be recognized by the irritability and activity of the palpons. In the adult they very often poke 



o 



O X 



o * 



o 



oc*>\+' 



XX ** 



cP,+ • 



00000 



X X X X X 



[I] 



[2] 



[3] 



W 



H 



Text-fig. 10. Diagrammatic representation of the possible steps in derivation of the 'Physophora' arrangement of 

 stem appendages [5] from that of Agalma [1] or vice versa, x = gastrozooid ; O = palpon; # = gonophore. 



Text-fig. 1 1 . Physophora hydrostatica. Sketches from life of A, resting position on bottom of glass vessel ; 



B, swimming posture. Nat. size. 



about amongst the nectophores, and their tips even enter the nectosacs. When swimming (Text- 

 fig. 11B) all the palpons are trained aft, their tips coming to a point outside the retracted tentacles. 

 The air-sac on its relatively long neck turns vertically upwards, the main axis being horizontal. It is 

 an active swimmer. A specimen measuring 6-5 cm. in length and having four pairs of fully developed 

 nectophores moved about 5-0 cm./sec. The rate of contraction of the nectophores in a closed vessel 

 at Villefranche on 28 April 1950 was about i/sec. In horizontal progression half of the nectophores 

 had their orifices facing upwards, and only these nectophores contracted in unison. The initial con- 

 traction when moving from the vertical resting position was made by the youngest nectophore. 



The simple tentacles of the palpons extended to about the same length as the palpons themselves, 

 namely an inch or more. When the animal sank, the tentacles of the palpons trailed upwards. At rest 

 they hung down inside the ring of palpons, which were of a rose-pink colour. The float was tipped with 

 a plum-coloured pigment. 



