308 COELENTERATA HYDROZOA chap. 



Apolemia — this genus attains a length of two or three metres. 

 Mediterranean Sea. Dicymlm, Indian Ocean. 



Physophorinae. — The pneumatophore larger in proportion 

 than it is in the preceding families. The stolon is sliort, and 

 bears rows of nectocalyces at the upper end. The gastro- 

 zooids, dactylozooids, and gonozooids are arranged in verticils 

 on the lower expanded part of the stolon. Hydrophyllia 

 absent. Phijsophora, cosmopolitan in the areas of warm sea 

 water. 



Fam. 2. Auronectidae. — The pneumatophore is large. The 

 stolon is reduced to a spongy mass of tissue on the under side of 

 the pneumatophore, and this bears numerous cormidia arranged 

 in a helicoid spiral. Projecting from the base of the pneumato- 

 phore there is a peculiar organ called the " aurophore," provided 

 with an apical pore. This organ has been described as a specially 

 modified nectocalyx, l)ut it is probably a specialised develop- 

 ment of the epithelium-lined portion of the pneumatophore of 

 other Physophorae. The Auronectidae . are found only at con- 

 siderable depths, 300 to 1-400 fathoms, and are probably specially 

 adapted to that habitat. Rliodalia, Stejohalia, Atlantic Ocean. 



Fam. 3. Rhizophysaliidae. — The pneumatophore is large, or 

 very large, in this family. The zooids are arranged in horizontal 

 rows on the under side of the pneumatophore {Physalia), or in a 

 helicoid spiral on a short stolon (Fj^ilmlia). There are no necto- 

 calyces nor hydrophyllia. 



The genus Physalia is the notorious " Portuguese Man-of-War." 

 The pneumatophore is a large bladder -like vesicle, sometimes 

 attaining a length of 12 cm. One species described by Haeckel 

 under the generic name Caravella has a pneumatophore 30 cm. 

 and more in length, and dactylozooids attaining a length of 20 

 metres. It is a curious fact that only the male colonies of 

 Physalia are known, and it is suggested that the female may 

 have quite a different form.^ Upihulia has a much smaller bladder 

 than Physalia. Both genera have a cosmopolitan distribution 

 at the surface of the warm seas. 



Fam. 4. Chondrophoridae. — This family stands quite by 

 itself in the sub-order Physophorae, and is placed in a separate 

 division of the sub-order by Chun, who gives it the name Tracheo- 

 PHYSA. The essential distinguishing characters of the family are 



^ Brooks and Coiiklin, Johns Hopkins Univ. Circ. x. 1S91, No. 88. 



