638 SUMMARY OF CURRENT RESEARCHES RELATING TO 



their extremity," and Zenker (in describing Acineta ferrum-equinum), 

 says " The internal canal of the arms is enveloped in two layers, one 

 internal, voluntarily contractile throughout its whole length and 

 muscular, so to say, in its nature, the other external, inert, mem- 

 branous, in continuity with the cuticular membrane of the animal." 

 On the other hand, Stein, Hertwig, and Fraipont describe the 

 tentacles as composed of clear homogeneous contents, enclosed in a 

 thin membranous wall. The author thinks that both these opinions 

 are true, and that according to the species, the tentacles may be con- 

 stituted with the two structures described by these authors. In 

 certain species (Splicerophrya magna, Acineta fcetida and A. emaciata), 

 the tentacles have a direct dependence on the peripheral zone of the 

 body ; in Hemioplirya gemmipara, on the contrary, they are organs 

 become completely independent of the integument, perforating the 

 latter and burying themselves in the substance of the body. Between 

 these two extremes we find, in Hemioplirya microsoma, an intermediary 

 arrangement in which the prehensile tentacles are a direct prolonga- 

 tion of the tegument, whilst the sucker tentacles are formed of inde- 

 pendent tubes, as in H. gemmipara. In very emaciated specimens of 

 Acineta fcetida, become very transparent, the author observed a 

 different disposition of the tentacles. The two fascicules were in- 

 serted at the extremity of a large tubular prolongation half invagi- 

 nated in a deep depression of the body, and projecting a little beyond 

 the opening of the shell. 



Having examined the structure of the tentacles and their relation 

 to the body, the author turns to the solution of the question to what 

 organs they can be compared in the general morphology of the 

 Protozoa. Are they sui generis or can any homologues be found ? 

 Koelliker, Haeckel, and Kent assimilate them purely and simply to 

 the pseudopodia of the Ehizopoda and Eadiolaria ; Stein and Claus 

 compare them to pseudopodia, but without affirming any real homo- 

 logy ; whilst Claparede and Lachmann, Hertwig, and Fraipont con- 

 sider them to be entirely different. Here, again, the author considers 

 that in all three views there is some truth if they are limited to 

 certain species instead of being generalized. There is a great resem- 

 blance between the tentacles and pseudopodia, both in regard to their 

 structure and their function, but he would not, nevertheless, consider 

 them as absolutely identical, the consequence of which would be to 

 class the Acinetidse with the Ehizopoda. They are organs of equal 

 morphological value, between which there does not exist any essential 

 difference of origin and nature and which consequently ought to be 

 considered as homologues in spite of the particular differentiations 

 which have managed to survive in certain types. 



The author has little to say of the nucleus, the structure and role 

 of which have been studied with so much skill by Hertwig, that sub- 

 sequent observers, such as Biitschli and Fraipont, have only confirmed 

 his observations. He adds, however, that the substance of the nucleus 

 is not always as homogeneous as in Hemioplirya gemmipara, and that 

 in it may be found a special histological structure, such as is seen in 

 that of Acineta Jolyi, containing numerous perfectly spherical vacuoles, 



