NOTES ON PLYMOUTH HYDROIDS. 



7 



is owing to an assumed necessity for free sarcode to explain 

 the pseudopodia-like processes on the free surfaces of the 

 sarcostyles. It seems to me that there is no logical demand 

 for free protoplasm to explain the great extensibility of these 

 organs. The possible tenuity of the walls of ectoderm cells 

 can be appreciated by any one who has made a study of 

 nematocysts, and a careful examination of the sarcostyles, both 

 living and in serial sections, has failed to afford any evidence 

 of free protoplasm, and this negative result is not antagonized bv 

 any physical necessity for free protoplasm in organisms which 

 can construct endoderm cell-walls of the marvelous tenuity 

 and extensibility of the nematocysts. 



The function of the nematophores is in more doubt than 

 their structure, and is not yet understood. It is practically 

 certain that they are more or less degraded "persons" of the 

 colony which have come to subserve definite functions of great 

 service, judging from the prevalence of these structures 

 throughout the Plumularidce. So far as the species under 

 consideration is concerned, it is safe to say that the sarcostyles 

 are not "fighting persons" or "machopolyps," because they 

 are not armed with any considerable number of nematocysts, 

 the special weapons of hydroids. An examination of the living 

 and active sarcostyles establishes the following facts — 



i. The almost incredible extensibility of these organs 

 which wind around the stem, branches, hydrothecae, and go- 

 nangia, in a perfect maze of threads, or even flattened lobate 

 masses. 



2. In retraction, the movement is not comparable to the 

 flowing of pseudopodia, but is effected by decided, quick, 

 jerky retraction, giving an idea of definite outlines and cohe- 

 sion. To use a crude comparison, the sarcostyle contracts 

 much as if it was made of stretched india-rubber and not of a 

 fluid. It is also worthy of note that there is no mechanical 

 entanglement of the various extensions of the sarcostyles, 

 although they appear to be hopelessly intertwined. 



3. The sarcostyles are particularly active in the vicinity of 

 mutilated or dead hydranths and gonophores, particularly the 



