35 o DISCOVERY REPORTS 



final branchlet. In Text-fig. 27 f the second pro-bud A 2 of fig. d has developed into similar terminal and 

 sub-terminal sections (A 2 1B , Ag 1 ^). 



New pro-buds always arise sub-terminally, and as a rule at a point opposite a jelly-polyp. Some- 

 times they form terminal-type, sometimes sub-terminal-type sections. PI. XXII, figs. 6 and 8 show 

 slightly later stages of development that might have been reached later on by the specimen shown in 

 Text-fig. 27 f. The first palpon, which is morphologically the terminal part of the branchlet, has grown 

 very much more rapidly than the sub-terminal parts. PI. XXII, fig. 11 shows how complicated the 

 young genital clusters look when the branchlets lie side by side. Those shown in PI. XXII, fig. 8 

 have been separated, flattened out and mounted on a microscope slide. 



PALPON 



JELLY- POLYP 



Text-fig. 26. Physalia physalis. Schematic drawing of a branch of a gonodendron to show repetitive pattern of growth. 

 br = branch, sub-term = sub-terminal section, term = terminal section. 



It will be noticed at this stage, which I call the Key-stage from a fancied resemblance to the lever- 

 steps of a simple key, that the buds of both terminal and sub-terminal sections stand out more or less 

 at right-angles to the long axes. In the next stage (PI. XXIII, fig. 2) they are more or less parallel to one 

 another and stand at an angle of 45 ° to the common axis. The jelly-polyps are no longer little conical 

 projections but have become more cylindrical; and the nectophore bud shows its medusoid nature. 

 The gonophores are now conspicuous objects. PI. XXIII, fig. 2 (right) may usefully be compared with 

 its earlier counterpart shown on the right-hand of PI. XXII, fig. 4. Stages of growth intermediate 

 between those shown in PI. XXIII, figs. 1 and 2 may be seen in PI. XXII, figs. 10, 11 . The most 

 mature stage of growth of branchlets of the gonodendron that I have seen is shown in PI. XXI, fig. 3, 

 which shows clearly (1) the jelly-polyp (jp) of the palpon (pt) of the terminal section, (2) the asexual 

 nectophore («) and palpon (ps.t) of the sub-terminal section, and (3) a number of female gonophores. 

 A rather less mature stage is shown in PI. XXI, fig. 2, where the mesogloea of the stalks of both 



