SYSTEMATIC AND BIOLOGICAL ACCOUNT 71 



hydroids, but I am not aware of any work that may have been done on gradient phenomena in other 

 coelenterate bud-colonies. That such phenomena occur, for instance, in Aglaophenid hydroids becomes 

 evident when the denticulation of the theca-margin from the stem-region to the tip of a hydrocladium 

 is examined; and there are axial gradients, too, from top to base of the colony. Lately I have 

 come across similar growth-gradient phenomena whilst making a tedious study of the bracts of 

 F. edwardsii, the Mediterranean species with the lemon-yellow spot on the velum. In no account of 

 any species of Forskalia can a satisfactory description or figures of the morphology be found, especially 

 of the bracts. 



Forskalia edwardsii Kolliker, 18536. 



In the spring of 1949, at Villefranche, I took the opportunity to anaesthetize and carefully preserve 

 parts of thirty-two large colonies of F. edzuardsii, and to obtain some photographic records 1 of the 

 living animal (PI. IV, figs. 4, 5, 8) — a very difficult procedure. Examination of a small, random sample 

 of the loose, preserved bracts of a specimen of F. edwardsii showed that it was easy to pick out bracts 

 of certain shape-categories, and that each category appears in two forms, one the mirror-image of 

 the other. Further examination of the specimen after staining — the bracts are very transparent — 

 showed that the stem bore leaf-like bracts, and that the long, muscular peduncles of the siphons, 

 so characteristic of Forskalia spp., carried bracts of at least three other kinds, the proximal pair being 



Cbr 



Jmm 



Text-fig. 29. Forskalia edwardsii. Bracts of a specimen captured at Villefranche, 31 March 1949, x 4. The three bracts, B, 

 are of a kind found only on the stem. C, a bolster-shaped bract found only on the upper part of the pedicels of the gastrozooids. 

 A, a series of eight stem bracts to illustrate constancy of shape. All bracts have enantiomorphs. Homologous points on the 

 bracts are lettered a, b, c. 



of the most simple form (Text-fig. 29 C). After making a series of camera-lucida drawings of numbers 



of each category, it was apparent that the shapes of bracts at different relative positions on the peduncle 



were fairly constant and characteristic. Finally I was able to homologize their structure. Though it 



appeared in life, while appendages, some of them almost invisible, were writhing about under the 



binocular, that there was no discernible ordered arrangement, it is now clear that all the bracts of 



F. edzvardsii have essentially the same structure, but that their proportions in different positions on the 



stem and peduncles vary markedly. The change in form takes place suddenly in passing from stem to 



peduncle, but progressively from the proximal to the distal end of each peduncle. It remains to be 



seen whether there is further progressive change from the anterior to the posterior end of the whole 



bud-colony. 



1 I have to thank Dr W. G. R. Marden for co-operation in this difficult task. 



