16 ARVID R. MOLANDER, ALCYONACEA. 
tinuation of the direct connection already existing in the case of this group, as a result 
of the reduction of the coenenchym. It proves, however, that the direct canal system 
is not at all a constant characteristic of Gersemia (sensu KUKENTHAL), which, on the con- 
trary, contains a number of species with preponderance of indirect canal system. It will 
be found from the following pages that Gersemia (sensu KUKENTHAL) cannot be consi- 
dered as a legitimate genus. The canal system shows the features characteristic of the 
respective species, according to the genera or families they belong to. 
Short Summary of the Development of the Canal System. 
The connection between the different polyps of the colony is effeeted by means 
of stolons. These are either simple (Cornularia) or contain endodermal canals and cell- 
strings (Clavularia). These stolons either run singly (Cornularia, Anthelia, Clavularia), 
or form membranes (Anthelia, Clavularia), which are the beginning of, and, later on, 
develop into a more or less ramified trunk. The development of a number of endodermal 
canals in the case of the Clavularia and Anthelia is the beginning of what is called indirect 
canal system, which connects the coelenterons of the polyps by means of numerous en- 
dodermal canals and cell-strings, which communicate with each other and with the coe- 
lenterons and produce the solenia. When the polyps are packed closer together, the 
connection may even become direct. On an altered formation of colony follows an altered 
canal system. In the case of Xeniidae, Alcyoniidae and Nephthyidae, the indirect canal 
system reaches a high stage of development. The coenenchym between the coelenterons, 
which corresponds with the mesenchymatic substance (= mesogloea) in the stolon, in 
the case of a Clavularia, is provided with numerous endodermal strings and canals, usu- 
ally placed vertically, which form a numerously branched solenia, connecting the polyps 
indirectly. This is, however, partly compensated for by wide, horizontal endodermal 
canals, which connect the coelenterons directly. These have developed secondarily 
from different causes, and are to be found both within Xeniidae and Alcyoniidae, and in 
Nephthyidae. "The chief cause of their origin has been the crowding together of and pres- 
sure among the polyps. This is the case with the great majority of specimens. Fur- 
ther, it is possible, as, for instance, in the case of Hunephthya groenlandica, that a vigor- 
ous development of spicules in the coenenchym may hinder the development of endo- 
dermal indirect canals and strings, direct canals being formed instead. 
The systematic classification has been based partly on the canal system. The 
existence of direct connection in particular has been adduced as a decisive factor. From 
what has been said above, it is shown plainly enough that any positive systematic con- 
clusions, based on this feature, are impossible. Variations within the same genus, in the 
same species at different stages of development, are often to be found. The indirect 
canal system is found within all genera and families dealt with here. 
