THE PLUMULARID.E. 25 



degradation towards the condition of undifterentiated protoplasm, in order that it may possess the faculty of emit- 

 ting pseudopodia t<> the extraordinary extent which we meet with in the sarcostyles of the Plumnlarinse ; so that even 

 though all the three body layers be present in the sarcostyles, we shall have in these appendages a portion which 

 can scarcely be distinguished from iinditJ'erentiated protoplasm. If this portion be not free protoplasm, it must be 

 sought for in the ectoderm. 



It should be remembered in this connection that every observer, so far as I can discover, who 

 has carefully studied properly prepared material for the investigation of sarcostyles has definitely 

 announced that the extensible processes are made up of ectodermal cells. The one modification 

 of this view is that of Merejkowsky, who announces that the cells were immersed, as it were, in 

 intercellular protoplasm. 



I know of no special investigations of the sarcostyles between 1888 and 1895, when the pres- 

 ent writer spent some time in the study of these remarkable structures at the Marine Biological 

 Laboratory in Plymouth, England, and the Zoological Station in Naples, Italy. As to the histo- 

 logical structures iie confirmed the conclusions of the later writers in most points. The sarco- 

 styles are composed of well-differentiated cells forming an ectoderm and an endoderm, separated 

 by a stutzlauielle. The arrangement of cells in Plumularia pinnata corresponds with that of Pin- 

 malaria halccioides as illustrated by Merejkowsky, the ectodermal cells on one side of the axis 

 being very much larger than those on the other. Muscular fibrilhe were found in Plumularia 

 pinnata and Antennultiria janiiui. There are few nematocysts in the sarcostyles of the Eleuthero- 

 plea so far as examined, but adhesive cells seem to play an important part. In several species 

 of Aglaophenia nematocysts were found forming formidable batteries just inside of the distal end 

 of the riern atop h ores (tig. 8G). 



In the Eleutheroplea the nematophores seem always to be of the simpler type, not being 

 divided into ueniatocyst-beariug and adhesive parts. In the Statoplea the ordinary arrangement 

 seems to be to have both these parts well developed and differentiated. 



I was not able to demonstrate the sense cells and ganglion cells of von Leudenfeld nor the inter- 

 cellular protoplasm of Merejkowsky. I do not consider, however, that this negative evidence 

 should weigh with any considerable force against the positive statements of such men as Harnann, 

 Weismaun, and the others quoted above. I am inclined to seriously doubt the existence of the 

 intercellular protoplasm, however, from the fact that the discovery of Merejkowsky is not con- 

 firmed by either of the three careful observers who immediately succeeded him, and is denied 

 positively by Weismaun. Hamaun's comparison of the pseudopodia of the cells of the foot 

 of the hydroida with those of the sarcostyles seems to me to be an apt one. I have myself seen 

 the living ectodermal cells of the somewhat protruded sarcostyle of Aglaophenia plum a send out 

 perfectly characteristic pseudopodia. It may be observed in this connection that under a high 

 power and careful manipulation of light it is sometimes possible to plainly distinguish the limita- 

 tions of the cells in the living sarcostyles. It would seem then that the ectodermal cells are them- 

 selves amoeboid and capable of conjointly exhibiting the wonderful extensibility so often described. 



A careful study of living and active sarcostyles yielded some results worthy of mention. Those 

 of P. pinnata proved particularly active in the vicinity of degenerating hydrauths and mutilated 

 gonangia (fig. 88). They advanced with a creeping motion over the sides of the hydrothec;e and 

 gouaugia, and into their cavities so as to suggest the idea that they might be acting as scavengers 

 for the colony. It could plainly be seen that the sarcostyles were adhesive, particularly at the ends of 

 the extensible processes, which would apparently cling to any object to which they became attached. 

 Then when the sarcostyles were contracted these ends would adhere until their resistance would 

 be suddenly overcome and the entire process retract with a jerking motion, the whole structure 

 behaving much like a rubber band attached by an adhesive end to some object and then torn 

 away by a pull on the rubber. The mesial sarcostyle of Aylaophenia helleri (fig. 89) seems to be 

 divided into three parts; one containing a battery of uematocysts and situated just inside of the 

 distal end of the nematophore; another, adhesive, which projects into the hydrotheca through 

 an opening leading from the adherent part of the uematophore; and a third, also adhesive, which 

 projects out from the top of the hydrotheca, crowding the nematocyst battery to one side. 



In studying the young gouosomal sarcostyles of Aglaophcnw pluma, it appeared that a new func- 

 tion was here exercised. The corbula under examination was in a very early stage of develop- 

 ment and the corbula leaves had not yet become adherent to each other along their edges, as is 



