24 AMERICAN HYDROIDS. 



Third. Sarcostyles with nematocysts and adhesive cells are exclusively found in the paired nemato- 

 phores of Aglaophenia.' 1 The lower pair of nematophores in Pentamlra were the ones which appear 

 to have been most successfully studied. These sarcostyles are composed of two parts a distal, 

 containing nematocysts, and a proximal, containing the adhesive cells and constituting the " adhe- 

 sive polyp." The latter portion is developed from the former. The endodermal axis and stutzla- 

 melle are wanting in the distal portion, but ganglion cells are found, together with radial muscle 

 cells and other cells which the author considers sense cells. The proximal or adhesive portion is 

 greatly extensible and contains an endodermal axis. The entire structure is merely a somewhat 

 complicated single sarcostyle, and not two joined together, as might be supposed. The sarcostyles 

 begin to develop long before the hydranth with which they are associated. At first they contain 

 no adhesive cells, their places being taken by nematocysts, but later they are found developing in 

 the supporting cells between the cnidoblasts, and increase, as it were, at the expense of the latter, 

 which lose their plasma investment, the nematocysts themselves finally disappearing. Still later, 

 when the adhesive cells are matured, there are yet a few single nematocysts on the adhesive part 

 of the sarcostyle. 



This author gives an interesting account of the action of living sarcostyles of this type. The 

 Plumularian captures the embryos of Crustacea (Zoea) as follows : The prey, coming in contact with 

 a tentacle of the hydrauth, is pierced by the tentacular nematocysts, which have a narcotizing 

 effect. Next it comes in contact with one of the adhesive bodies at the end of the greatly pro- 

 duced sarcostyle. The adhesive cells adhere to the prey, and the body of the adhesive polyp 

 quickly retracts, bringing the Zoea into contact with more of the globular adhesive masses, which 

 hold it in spite of even the most violent struggles for liberty. It is thus brought again within 

 range of the tentacles and devoured. The adhesive cells are finally cast off, remaining attached 

 to the victim, and the sarcostyles again retract. 



When a large animal, such as an Annelid, strikes the tentacle, the adhesive threads immedi- 

 ately retract, as do also the tentacles, anil the batteries of nematocysts on the other part of the 

 sarcostyles are brought into play to repel the attack (fig. 83). 



The author regards the nematocysts and adhesive cells as homologous structures, and believes 

 that they are not gland cells, but a secretion of gland cells, a product thrown off 1 from the organ- 

 ism and of no further utility. Von Lendenfeld does not seem to have encountered anything like 

 the intercellular protoplasm of Merejkowsky. It seems probable that the unicellular glands of 

 the latter are much the same as the adhesive cells of von Lendeufeld. 



Dr. Carl F. Jickeli, in his second paper on Der Bau der Hydroidpolypeu, 2 discusses the 

 sarcostyles more briefly than the other writers. He does not seem to have seen the works of 

 Merejkowsky, Weismaun, or vou Lendenfeld. He concludes that the sarcostyle is homologous 

 with the solid tentacle of the hydranth, with an axis composed of endodermal cells. He regards 

 the tentacular organs of Ophiodes as sarcostyles, and considers them as homologous with the 

 capitate tentacles of many hydroids, and thinks it possible to tiud the iutergradation between 

 scattered sarcostyles and the complete tentacle whorl of the Plumulariau hydranth. He seems 

 to regard the sarcostyle of Aglaophenia, with its distal defensive and proximal adhesive parts, 

 as a two-tentacled sarcostyle, a suggestion with which no authority that I have consulted would 

 be likely to agree. 



This author finds an objection to regarding the sarcostyles as weapons of the colony in the 

 fact that they are most abundant where, in his opinion, they are least needed that is, in the vicinity 

 of the hydranths, which are sufficiently protected by the ueinatocysts in the tentacles and are 

 wanting in the delicate twig terminations, where, he thinks, they would be most effective. 



In 1888 the second part of the report of the Challenger collection of hydroids appeared, in 

 which Professor Allman says: 3 



We have, however, already seen that the ectoderm, in the modified condition which it often presents in the 

 coenosarc, may show an entire obliteration of cell boundaries and may throw out processes having many of the. char- 

 acters of true pseudopodia, and it needs hut a further modification of this layer, consisting in a still lower grade of 



'The species more especially studied by this author was Pentandra parvuJa, a form which von Lendenfeld at 

 one time regarded as Aglaophenia parvuJa Bale. It is characterized by having two pairs of paired nematophores and 

 a single mesial nematophore in connection with each hydranth. 



-Der Bau der Hydroidpulypeu, Morphologisches Jalirbuch, 1883, VIII, pp. 580-680. 



Report on the Hydroida dredged by H. M. S. Challenger during the years 1873-1876, Second Part, 1888, pp. six, xx. 



