OP ARTS AND SCIENCES. 281 



method of origin and structure, one finds it difTicult to concur with the 

 suggestion of Professor Ehlers, that the coUare setosum of Cteuosto- 

 mata is homologous with the cirri of Endoprocta. Muscles and fu- 

 niculi both arise from the cells of the coelomic epithelium. The 

 communication plates arise as a circular fold of the body-wall. The 

 cells of the coelomic epithelium which immediately surround the cen- 

 tral pole become metamorphosed at their inner ends to form the teeth 

 of the central sieve. 



The polypides of the Bicellariidce ^ Membraniporidce, and Alcyoni- 

 diidce arise in a similar manner to those of Paludicella; that is, from 

 a mass of inditferent cells at the margin of the colony, — a mass from 

 which the body-wall also is derived. The polypide arises in all cases 

 by an invagination of the body-wall, which is two-layered at the mar- 

 gin of the colony. In all cases studied, the whole of the jtolypide 

 is derived from this one rudiment. The alimentary tract arises, at 

 least in some cases, exactly as in Paludicella. The ganglion arises 

 from the inner layer of the bud, by an evagination of the floor of the 

 atrium in both Ctenostomata and Cheilostomata, and I have found no 

 trace of a genuine epistome at any stage. 



Budding in marine Gymnoloemata seems to occur in accordance 

 with certain laws, which may be deduced from a study of erect colo- 

 nies like Bugida. In Bugtda turrita, Verrill, we have a colony with an 

 erect axis and branches whose points of insertion he m a right or left 

 handed spiral. The phyllotactic arrangement of the branches is not 

 an invariable one, but is approximately §. Each branch is fan-shaped, 

 the handle being the point of attachment, and is slightly concave to- 

 ward the axis, like the thread of an Archimedean screw. The fans 

 at the base of the colony are largest and oldest, at the tip youngest. 

 The individuals are arranged end to end, in lines which spring from the 

 single most proximal individual, and increase in number as upon this 

 and the successively more distal individuals lateral as well as terminal 

 buds arise. Sometimes, however, but one new bud — a terminal one — 

 arises. The branches are not wholly separate from each other, but 

 cling together in pairs. 



The following laws of growth have been deduced : — 1 . The indi- 

 viduals " break joints." 2. The lateral buds are formed earlier, and 

 do not extend so far distally as the terminal buds. 3. When a termi- 

 nal and lateral bud attached to the same proximal individual are each 

 immediately followed by two buds, the two lateral buds lie adjacent, 

 the two terminals outside. 4. Lateral buds tend to arise at the same 

 time on two branches which spring from a common individual. 5. Law 

 4 is modified by a superior one, according to which lateral buds arise 



