AMERICAN HYDROIDS. 



SECTION I.-THE 



MORPHOLOGY OF THE PLUMULAEiD^E. 



Only the more distinctive features of the Plumalaridae will be discussed, here, the intention of 

 the author being to reserve the presentation of the morphology of the Hydroida as a whole lor the 

 general introduction to this work, which will accompany the last section. 



In pursuance of this plan the several structures more or less characteristic of the family 

 Plumularida- have been studied with special care. The most important of these are the iieuia- 

 tophores, sareostyles, and the assemblage of structures known as gouangia, phylactocarps, and 

 corbula-. The morphology, use, and homologies of these organs will be discussed at considerable 

 length. The Plumularidiu have been regarded as of special interest by nearly all writers on the 

 Hydroida, and their characteristic features have been carefully studied and described by a number 

 of our ablest naturalists, of whom Hincks, Alluiau, and Bale should be particularly mentioned as 

 most prominent among British writers. Continental naturalists also have contributed largely to 

 our knowledge, especially Kirchenpauer, von Lendenfeld, Hamaun, Jickeli, Merejkowsky, and 

 Weisuiaun. The works of these and other authors will be discussed and proper references given 

 in the following pages. 



My own investigations were carried on mainly in the Marine Biological Laboratory, Plymouth, 

 England; the Naples Zoological Station, Naples, Italy; the Laboratory of the U. S. Fish Commis- 

 sion, Woods Hole, Massachusetts, and at Dr. Alexander Agassiz's private laboratory, Newport, 

 Rhode Island. At all of these places material and equipment were abundant, and the facilities 

 for studying living hydroids all that could be desired. 



TliOPIIOSOME. 



Among the Plumularidat there is a greater number of simple uoubranchiug forms than in the 

 other families of the Hydroida. The name Plumularid;e itself suggests the most common outline of 

 the colony, which ordinarily consists of the single upright stem with laterally disposed ultimate 

 branchlets, or "pinna 1 ," or " hydrocladia," as they are more commonly designated, the whole 

 resembling in general form a plume or feather, which it fully equals in grace and symmetry. The 

 main stem may arise from a tangled mass of filamentous rootlets, or from a creeping rootstock, 

 which grows over alga-, stones, shells, or any other convenient base for support. A number of 

 these delicate fronds may grow together, forming a plumose tuft resembling a miniature clump of 

 ferns. Many species have a more or less pronounced branching habit, assuming various modes 

 of ramification, dendritic, alternate, or opposite, the most common subdivision being in the form 

 of pinnately disposed branches, giving the whole colony a flabellate outline. Those forms having 

 simple nonfascicled stems are not apt to branch profusely, the greater portion of the decidedly 

 branching species being characterized by the fascicled stem presently to be described. The most 

 thoroughly dendritic species known to me is Plumularia ilcnth-itii-a from the Bahamas, which 

 divides again and again into scores of brauchlets and terminal twigs. Many species give forth 



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