SYSTEMATIC AND BIOLOGICAL ACCOUNT 45 



Garstang tried to analyse the structure and development of Physophora, one of five types of brachy- 

 stele Physonects, Rhodalia, Physophora, Athorybia, Epibula and Nectalia. He had, perforce, to rely 

 on very unsatisfactory, old and partly restored figures for developmental stages. Thanks to a generous 

 grant from the Browne Fund which I received in 1949 from the Royal Society, I was able to study 

 alive at Villefranche two mature and some dozens of developmental stages of this species. There was 

 a great deal of other work to be done at Villefranche and it was only recently, after staining the 

 anaesthetized and fixed larvae, and after examining young specimens from La Jolla and others taken 

 in 1951 by 'Scotia' off North-west Ireland, that I was able to gain a more correct idea of the mor- 

 phology and ontogeny. It would not be profitable to mention all the mistakes that have been made 

 in the interpretation of the morphology and development of this species. Haeckel was not, I think, able 

 to distinguish the different types of bud from one another, so that his figures of developmental stages 

 do not make it clear which are palpon-, gastrozooid- and nectophore-buds. His ' Challenger ' figures of 

 larvae give the erroneous impression that the pneumatophore is contained in the mesogloea of the bract. 



How to orientate the larva is a puzzle. In one place Haeckel calls the bracteal cleft dorsal, as does 

 Garstang, and in another ventral. Perhaps the meridian in which the second gastrozooid is budded, 

 close to that in which the first palpon is budded, and near the bracteal cleft, might be called ventral, 

 and the region of attachment of the nectophore buds dorsal. The meridian, in which the tentacle of 

 the protosiphon (first gastrozooid) and bract lie, would then be close to the ventral. But there are no 

 two well-marked and opposite meridians. The function of the bract seems to be to provide cover for 

 the retracted tentacle. 



The picture Garstang gave of a young stage of development was that of a protosiphon hanging down 

 from the middle of a basal stem surface. This consisted of a wide space surrounded by a ring of palpons. 

 Round this open space he pictured the buds of siphons, gonodendra, and other palpons circulating, 

 with much jostling and squeezing, as they advanced from a marginal budding zone in three parallel 

 whorls, grouped into cormidia along the meridians. My own observations show that this is not a good 

 picture of what takes place. There is no open space until after most of the appendages have been 

 formed and have grown apart. The first palpons are not, I believe, budded regularly in one meridian, 

 though the last formed ones may be. For instance, palpon II appears commonly to be budded to the 

 right of palpon I, palpon III to its left and palpon IV between I and II. Later on, palpon-buds appear 

 in other meridians, between and distal to earlier formed ones. The second gastrozooid is budded quite 

 early on, when there are only two or three palpons. When the bract drops off, its position is taken by 

 palpons, which by that time form a complete ring. The first palpons are budded from a region on the 

 apical side of the constriction that separates the pneumatochone from pneumatosaccus, at a time when 

 the pneumatochone extends down to the level of the distal end of the basigaster. As the growth of 

 the budding zone of the nectophores carries the pneumatophore upwards and away from the ring of 

 the palpons, the external wall, to which they are attached, increases in diameter, but not to an equal 

 extent in all meridians. The radius of curvature increases steadily as we pass from the growing point. 

 At first sight, it might be thought that the marginal area, to which palpons are attached, should be 

 regarded as part of the nectosome, because of their relative larval position. But this area is not 

 muscular like the nectosome proper. Since there is virtually no special growing zone between the 

 level of attachment of the palpons and the base of the protosiphon, there is little to compare with 

 the siphosome of Macrostelia. Any argument, therefore, as to whether the siphosome in Physophora 

 forms a twisted stem round an imaginary central axis is unnecessary. But if the basal part of the proto- 

 siphon was extended by a growing zone, we should get something very like a macrostele stem. Examina- 

 tion of hundreds of larvae of Nanomia bijuga 1 , a macrostele, shows that the budding zone of the 



1 Commonly known as Stephanomia bijuga. 



