THE PLUMULARID^E. 23 



suit the work of the others, 1 and only one of them had the advantage of consulting Merejkowsky's 

 paper, and that was Weismann. 



Weismaun, 2 in his discussion of Pluinularia- echinulata, agrees with Hamann and Merejkowsky 

 in describing the sarcostyles as composed of ectoderm cells surrounding a solid endodermal 

 axis, the two layers being separated by the stutzlamelle. He considers the sarcostyles as degen- 

 erate polyps. He takes issue, however, with Merejkowsky concerning the free intercellular 

 protoplasm in the sarcostyle. He thinks that the phenomena concerning the pseudopodial 

 processes are similar to those frequently observed in the ectoderm of the stem, which greatly 

 resembles free protoplasm in its appearance and movements while living, but proves strictly cellular 

 when examined after staining and sectioning. 



By far the most complete, investigation of the sarcostyles that has yet appeared was published 

 in that same year (1883) by von Leudent'eld. 11 He had an excellent opportunity to study the active 

 sarcostyles of many living Australian Plumularida-. The following is a condensed translation of 

 the more important points ascertained by von Lendeufeld: 



The author agrees with Hamann that the sarcostyle (Wehrthiere) is a modified polyp. He 

 divides the sarcostyles into three classes, as follows: 



First. Sarcostyles with nematocysts (fig. 82) characteristic of the genus Plumularia, consisting 

 of a solid endodermal axis composed of cells much like the axial cells of the solid tentacles of the 

 hydranths, and an ectoderm composed of two layers, epithelial and subepithelial. In the latter or 

 subepithelial layer is a bundle of muscle cells. Between the ectoderm and the endoderin is a 

 dividing membrane or stutzlamelle. The muscle cells combined constitute a cylinder embracing 

 the distal part of the axis, but outside of the stutzlamelle. Several large ganglion cells are found 

 in the subepithelial layer at the end of the axis. Large curved nematocysts lie in the endo- 

 thelium, each being partly inclosed in a plasma investment with a flat nucleus. The distal end of 

 the plasma layer of each nematocyst cell is produced into a long process. All of these processes 

 are concentrated at the very spot where the ganglion cells He. There are sometimes radial muscle 

 cells in which are situated the thick handles of the cnidoblasts. The author regards some of the 

 surface cells as sense cells. The expansion of these sarcostyles is much more rapid than their 

 retraction, the movements being like that of a solid tentacle, but slower. The tentacles are of far 

 older phylogeuetic structure than are the sarcostyles. Transition between a Protohydra and a 

 sarcostyle consists of a gradual pressing back (zuruckdraugeu) of the digestive cavity, resulting 

 first in solid tentacles and then in a growing together of the body walls. Sarcostyles are defensive 

 weapons because they are most active when the colony is disturbed, but they are also employed 

 in the capture of food. In all cases examined the nematocysts remain in the distal end of the 

 sarcostyle, accompanying the latter in its movements. 



Second. Sarcostyles with adhesive cells are found particularly in the mesial nematophores of 

 Aglaophenia, but also in Flumularia. These sarcostyles are similar to the first kind, but have 

 adhesive cells in place of nematocysts. These adhesive cells are considered to be identical with 

 the snare threads (Faugfaden) or prehensile cells of Ctenophores. The "adhesive polyps" are 

 very mobile, being capable of extending themselves into long fine threads, each ending in an 

 enlargement, which is itself capable of considerable change, of form (fig. 85). Surface cells, sub- 

 epithelial muscle cells, ganglia, and an endodermal axis are present. The distal portion consists of 

 crowded pyramidal cells (fig. 84) radially arranged, and with adhesive bodies in the shape of 

 rounded highly refractive globules. The cells resemble glandular cells, and the globules originate 

 in the narrow proximal part of each cell and migrate during their development toward the distal 

 wider ends of the cells, finally protruding through the upper surface. These are the adhesive 

 cells which occur in considerable numbers on the distal end of the sarcostyle. They differ from 

 the similar structures in the Ctenophora in not having the thread spirally coiled. The author 

 has seen these sarcostyles with an appearance of branching, due to the fact that one or more 

 adhesive cells, having become attached to some foreign object, remain connected by a very fine 

 thread upon the retraction of the sarcostyle. 



1 Weismann includes Jifkeli's work in his bibliography, but it evidently appeared ton late to be consulted in 

 the preparation of the text. 



-Die Entstehuug der Sexualzellfn bei den Hydroraedusen, Jena, 1883, pp. 175, 176. 



:1 Uelier Cn-leuterateu der Siidsec, III. Mittheilungen Ueber Wehrpolypeii und Nesselzellen, Zeitschrift fiir 

 wissenschaftliche Znologie, XXXVIII, 1882, pp. :!.". :!T|. 



