No. 376.] SARCOSTYLES OF THE PLUMULARIDZ. 225 
Allman. This author regards the sarcostyles as degenerate 
individuals of the hydroid stock, serving the purpose of defen- 
sive organs and possibly also as aid in the nourishment of 
the colony. 
Weismann, in his Die Enstehung der Sexualzellen bei den. 
flydromedusen, denies the presence of the interstitial proto- 
plasm in the ectodermal portion and contends that the pseudo- 
podia are from the ectoderm cells themselves. 
In the same year, 1883, von Lendenfeld t made a very elab- 
orate study of the sarcostyles. In addition to the ectoderm, 
endoderm, and “ Stutzlamelle’”’ already mentioned, he found a 
differentiated ectodermal muscle layer, in which are large gan- 
glion cells in Plumularia. In certain species of Aglaophenia and 
Plumularia he found sarcostyles furnished with adhesive cells 
similar to those found in ctenophores, but differing from them 
in not having a spirally rolled thread. 
Dr. Carl F. Jickeli? agrees with most of the other writers 
concerning the histology of these structures, but has a unique 
idea of their homology. He thinks that the sarcostyles are 
homologous with the capitate tentacles of many species of 
hydroid polyps. I believe that he has no supporters in this 
view. 
No other investigations of sufficient importance to discuss in 
this connection have been made so far as I know, with the 
exception of my own work in 1895 at Plymouth, England,’ and 
at Naples, where I made careful studies of these structures in 
the living plumularians and by means of serial sections. 
The histology of the sarcostyles, as held by most of the 
above writers, shows an outer layer of ectoderm and an inner 
layer of endoderm, these two layers being separated by an 
apparently structureless membrane called by the German 
writers the “ Stutzlamelle.” The endodermal layer appears to 
be a solid core in stained and sectioned preparations, and is so 
described by most writers. Under favorable conditions living 
1Ueber Wehrpolypen und Nesselzellen. Zeit. f. wiss. Zool, Bd. xxxviii, pp. 
355-371 2 Morphol. Jahrb., Bd. viii, pp. 580-680. 
2 See C. C. Nutting, Notes on Plymouth Hydroids. Journ. Marine Biol 
Assoc., February, 1896, p. 153- 
