Sarcostyles of the Plumularidae. 119 



This author considered that these processes were composed of 

 protoplasm, pure and simple. 



When, however, the more refined and modern histological 

 technique was applied by Hamann to the investigation of the 

 sarcostyles, it was discovered that they were much more com- 

 plicated structures than was at first supposed ; that they were 

 made up of several histological elements, namely, an ecto- 

 dermal layer surrounding an axial portion composed of endo- 

 dermal cells, the ectoderm and endoderm being separated by a 

 structureless membrane or " Stutzlamelle." The distal part 

 of the sarcostyle contains nematocysts or nettling cells. This 

 author (Hamann *) concluded that the enormous extensibility 

 of the sarcostyle was due to muscle-fibrilla?, and regards the 

 entire sarcostyle as a degraded person or hydroid polyp in 

 which the mouth and body-cavity have been obliterated. 



In the same year (1882) C. de Merejkowsky f announced 

 that the histological elements were ectoderm and endoderm 

 with a dividing membrane, and that the motile part was com- 

 posed of ectoderm alone, the ectodermal cells being immersed 

 in a contractile structureless protoplasm. To this latter sub- 

 stance he attributed the enormous extensibility of the sarco- 

 style and the pseudopodia-like processes originally described 

 by 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 beiden 

 Hydromedusen,' 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 J made a very 

 elaborate study of the sarcostyles. In addition to the ecto- 

 derm, endoderm, and " Stutzlamelle " already mentioned, he 

 found a differentiated ectodermal muscle-layer, in which are 

 large ganglion-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 



* " Der Organismus der Hydroidpolypen," Jenaische Zeitsch. f. Naturw. 

 Bd. xv. pp. 17, 18, 65. 



t Arch, de Zool. exp. et g6n. vol. x. pp. 583-610. 



\ " Ueber Wehrpolypen uud Nesselzellen," Zeit. f. -wis*. Zool. 

 Bd. xxxviii. pp. 355-371. 



§ Morphol. Jahrb. Bd. viii. pp. 580-680. 



