X CALYPTOBLASTEA LEPTOMEDUSAE 277 



protect an indefinite person, an individual that may become either 

 a sarcostyle ^ 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 dactylo- 

 zooids 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, Lafo'eina, Oplorliiza, Perisiphonia, Diplo- 

 cyathus, 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. 



In a very large number of Calyptoblastea the gonophore is a 

 reduced Medusa which never escapes from the gonotheca, but in 

 the family Eucopidae the gonophores escape as free -swimming 

 Medusae, exhibiting certain very definite characters. The gonads 

 are situated not on the manubrium, as in the Anthomedusae, 

 but on the sub-umbrellar aspect of the radial canals. The 

 marginal sense-organs may be ocelli or vesiculate statocysts. 

 The beU is usually more flattened, and the velum smaller than 

 it is in the Anthomedusae, and the manubrium short and 

 quadrangular. Such Medusae are called Leptomedusae. 



Leptomedusae of many specific forms are found abundantly at 

 the surface of the sea in nearly all parts of the world, but with 

 the exception of some genera of the Eucopidae and a few others, 

 their connexion with a definite Calyptoblastic hydrosome has not 

 been definitely ascertained. It may be an assumption that time 

 will prove to be unwarranted that all the Leptomedusae pass 

 through a Calyptoblastic hydrosome stage. 



1 The term "sarcostyle" is usually applied to the dactylozooid of the Calypto- 

 blastea. 



