In some genera there are special modifications of the branches and hydrocladia, for the protection of the gonothecae. The name "Phylactocarp" is used to designate structures that are obviously intended to serve this purpose. The phylactocarp of the genera _Aglaophenia_ and _Thecocarpus_ is the largest and most remarkable of this group of structures, and has received the special name "corbula." The corbula consists of an axial stem or rachis, and of a number of corbula-leaves arising alternately from the rachis, bending upwards and then inwards to meet those of the other side above, the whole forming a pod-shaped receptacle. The gonangia are borne at the base of each of the corbula-leaves. There is some difference of opinion as to the homologies of the parts of the corbula, but the rachis seems to be that of a modified hydrocladium, as it usually bears at its base one or more hydrothecae of the normal type. The corbula-leaves are usually described as modified nematophores (_vide infra_), but according to Nutting[315] there is no more reason to regard them as modified nematophores than as modified hydrothecae, and he regards them as "simply the modification of a structure originally intended to {277}protect an indefinite person, an individual that may become either a sarcostyle[316] or a hydranth." The other forms of phylactocarps are modified branches as in _Lytocarpus_, and those which are morphologically appendages to branches as in _Cladocarpus_, _Aglaophenopsis_, and _Streptocaulus_. The structures known as "nematophores" in the Calyptoblastea are the thecae of modified zooids, comparable with the dactylozooids of _Millepora_. They form a well-marked character of the very large family Plumulariidae, but they are also found in species of the genera _Ophiodes_, _Lafoëina_, _Oplorhiza_, _Perisiphonia_, _Diplocyathus_, _Halecium_, and _Clathrozoon_ among the other Calyptoblastea. The dactylozooids are usually capitate or filiform zooids, without tentacles or a mouth, and with a solid or occasionally a perforated core of endoderm. They bear either a battery of nematocysts (_Plumularia_, etc.), or of peculiar adhesive cells (_Aglaophenia_ and some species of _Plumularia_). The functions of the dactylozooids are to capture the prey and to serve as a defence to the colony. In the growth of the corbula of _Aglaophenia_ the dactylozooids appear to serve another purpose, and that is, as a temporary attachment to hold the leaves together while the edges themselves are being connected by trabeculae of coenosarc.