4 THE ZOOLOGIST. 



survival than those which did not, but they would less quickly 

 spread the species over a wide area. 



The remarkable persistence of types like Cliona, which not 

 only form branches freely, but bore in calcareous rocks and 

 shells, is a striking feature in the group. The moniliform and 

 branched tunnels in dead shells are conspicuous on the celebrated 

 shell-beach at Herm ; besides boring in living shells, it is thus 

 one of the main agents in disintegrating shells on the sea- 

 bottom. Their beautifully dendritic patterns — with the enlarge- 

 ments where the oscula occur — are well seen in the very thin 

 lower valves of southern Anomice, which are too thin for the 

 boring of any known annelid, and especially of the cosmo- 

 politan Polydora. A distinguished author formerly held that 

 sponges did not bore, but only took possession of the tunnels of 

 such annelids as Polydora in shells and rocks. A very thin 

 (almost like paper) lower valve of Anomia was sent to him in 

 spirit without remark. When held to the light the moniliform 

 and finely branched tunnels of Cliona were clearly seen with the 

 oscula at the enlargements. Nothing could have been more 

 convincing, and, so far as known, no further remarks on the 

 subject were made. 



In no group is budding more conspicuous than in the hydroid 

 stocks of the Ccelenterates, as shown in the simplest condition in 

 such as Hydra, and in a more complex manner in the plant-like 

 tufts of the hydroid zoophytes, which are either dimorphic or 

 polymorphic. As the food-canal of the entire colony is con- 

 tinuous, it is evident that by this process of branching the 

 balance is more or less maintained, since new mouths and 

 additional predatory tentacles spring into existence with the 

 other parts of the organism. Moreover, great variation occurs 

 in the nature of the buds, which Arnold Lang calls the sisters of 

 the nutritive polypites ; for, whereas in some the buds con- 

 taining the eggs and sperms remain attached, in many they 

 swim freely as the delicate glassy circles — the familiar jelly- 

 fishes or hydro-Medusae — so that buds from the most distant 

 parent-stocks commingle. And, as if even these steps were not 

 sufficiently complex, we find that in certain species (Codonium, 

 Lizzia) these transparent swimming jellies give off others by 

 budding from the stalk (manubrium), or from the edge of the 



