THE PLUMULAU1U.E. 45 



greatly elongated and enlarged, the proximal part of this extension being divided into a great 

 number of short internodes, while the distal portion was abruptly bent over so as to form a nearly 

 closed hook (tig. 124). In many cases the ends of two colonies would be hooked together, 

 clasping each other so tightly that they could not be separated without mutilating the specimens 

 (fig. 122, <). This state of affairs was so common at this time that one could not regard the 

 attachment as accidental or abnormal, and further developments were awaited with great interest. 



In July this attachment was seldom seen, although the enlarged stein terminations were still 

 common. These latter appeared to be shedding their perisare, which was often seen to be partly 

 peeled off. 



About the middle of August I observed that these enlarged ends were for king just as did the 

 produced hydrocladia of P. pinnnta (fig. 124). Still later, immediately before my departure from 

 Naples, I found some of these enlarged ends attached to the sides of the jar and budding, although 

 the buds had not yet developed into hydranths. There is practically no doubt that we have here a 

 case of stoloniferous reproduction in the genus Aglaophcnin. 



Although I was unable to demonstrate the use of the clasping hooks at the ends of the stems 

 it was impossible to escape the constantly recurring suggestion that they might possibly signify 

 a mode of conjugation such as is found among the Protozoa(for example, 1'arameci urn) and the Alga- 

 (for example, Spirogyra). 



That these hooked ends are for some definite purpose can be confidently assumed, and there 

 are but two explanations which appear plausible. 



First. These terminal hooks may aid directly in the stoloniferous reproduction by attaching 

 themselves to some adjacent object upon which the new colonies can grow. 



Second. They may be clasping organs for use in conjugation. As a matter of fact they may 

 serve both purposes. My observations strongly indicate that they are useful as a means of attach- 

 ment, and the following considerations indicate a strong possibility that conjugation may take 

 place. 



First. They were seen so often in a position favoring conjugation, that is, with the ends of two 

 colonies clasped in a close embrace, as to indicate a normal function. 



Second. It was after this supposed conjugation that the stoloniferous multiplication was 

 observed to be under way. 



Third. These enlarged ends of the stems were found to contain a number of aui<rboid cells 

 which were unusually active, sending out pronounced pseiulopodia. I could not decide definitely 

 whether these cells were in the ectoderm or endoderm, on account of the unfavorable position of 

 the living colony under inspection. 



Stained sections of these hooks failed to throw much additional light on the subject, the only 

 noticeable histological feature being an appearance of great activity in cell multiplication and 

 the presence of an unusual number of nematocysts. These sections were of value, however, in 

 demonstrating that the enlargement of the stem termination was not due to the presence of a 

 parasite, as is sometimes the case among hydroids, for example, Syncwyiic c.runiu and Cm-i/iic 

 mirabilis. 



The clasping of the hooks is probably effected mechanically by the undulations of the ripples 

 passing along the alga which supports the hydroid colonies. 



Conjugation is essentially the union of two individuals of a species during which an inter- 

 change of protoplasm is effected without the intervention of ova or spermatozoa. So far as I have 

 been able to discover, this process has not heretofore been found among the meta/.oa, 1 and the 

 observations recorded above must be regarded as merely an indication of the possibility of conju- 

 gation among hydroids. 



It is now a well established fact that the sex cells, both male and female, of the Plumularidse 

 originate in the endoderm of the stem; and any process which would enable the contents of the 

 endodermal cells of one stem to mix with the contents of the endodermal cells of the stem of 

 another colony would render conjugation possible so far as the purely mechanical part of the 

 question is concerned. This would be effected in the case under consideration by the solution of 



'The perraauent union of individuals which results iu l)iplo:oon can not In- termed cnujn^atiiiii in Hi.- sense li.-re 

 used, because in the Diplozoon the Intervention of ova and spermatozoa occurs. 



