18 



POLYPIFERA. 



with the kind of fissiparous division which the 

 animalcules undergo. At certain periods four 

 of these saccuii are met with in several of these 

 Infusoria, whilst at others only two are found 

 in animalcules of the same species. When 

 four are present, there are always two situated 

 in each half of the body, and it is remarkable 



1 & 4. Paramecium aurelia. 2, 3. Kolpoda cucullus. 



, $, contractile vesicles ; t, testes ; o, oral opening ; 



a, anal opening. (After Ehrenberg.) 



that all the Infusoria thus furnished are suscep- 

 tible both of transverse and longitudinal divi- 

 sion, so that when so divided each quarter 

 retains one of these organs. In Euodon cucul- 

 lnhts three of these vesicles are present, two of 

 which are placed one on each side of the dental 

 cylinder, and the third in the hinder part of the 

 body near a dilatation of the alimentary canal 

 in the vicinity of the anal opening. This ani- 

 nwlcule likewise divides both longitudinally 

 and transversely. 



There is another organ regarded by Ehren- 

 berg as playing an important part in the organi- 

 zation of these Infusoria. This is of a roundish 



Fig. 19. 



Euplotes Charon, exhibiting its different modes of 

 fissiparous generation. (After Ehrenberg.) 



form, but less transparent than the contractile 

 sacculus in the neighbourhood of which it is 

 situated, but its presence has only been de- 

 tected in four or five species. With respect to 

 the functions to be ascribed to the parts above 



described, it is by no means easy to come to any- 

 satisfactory conclusion. Ehrenberg considers 

 that the contractile organs provided with their 

 radiating canals cannot be regarded as hearts 

 because their movements are so slow ; neither 

 can he regard them as respiratory organs, which 

 would require the presence of a vascular appa- 

 ratus more distinctly developed than it appears 

 to be in the Polygastric animalcules ; he is, 

 therefore, disposed to believe them to be con- 

 nected with the generative system, and refers to 

 them the office of fecundating the ova con- 

 tained in the interior of the body by dispersing 

 the seminal fluid. 



The opaque body above described, the same 

 authority suggests to be the testis, believing it 

 to secrete a seminal fluid. Both these suppo- 

 sitions are based upon a fancied analogy be- 

 tween the parts in question and certain organs 

 which are met with in the Rotifera, and it is 

 needless to say that they are at present purely 

 hypothetical. (T. Rymer Jones.) 



POLYPIFERA. A class of Zoophytes 

 most extensively distributed over the surface 

 of the globe, inhabitants both of the ocean 

 and of fresh water, and important both on 

 account of their numbers and of the magni- 

 tude of the structures raised by their agency. 

 The most obvious character common to this 

 vast race of animals is, that their mouths are 

 surrounded by radiating tentacula, arranged 

 somewhat like the rays of a flower ; and hence 

 the terms ZOOPHYTA, PHYTOZOA, and AN- 

 THOZOA, have been more especially applied 

 by naturalists to the members of this group 

 of living beings. So plant-like, indeed, are 

 the forms of many genera, that the ancients 

 regarded all the stony polypes as stony vege- 

 tables, or as vegetating stones, and invented 

 many theories to explain their growth. The 

 earlier modern naturalists thought them plants, 

 and even Tournefort has described twenty- 

 eight species in his " Institutions of Botany ;" 

 but he was the last naturalist who committed 

 this grave error. The animal nature of the 

 Polypes was suspected by Imperato in 1669, 

 was proved by Peyssonel in 1727, and shortly 

 afterwards confirmed by Reaumur and Jussieu, 

 the latter of whom, in 1741, added them to 

 the animal kingdom.* In order to facilitate 

 our investigations concerning the anatomy 

 and physiology of so extensive a series of 

 organized beings, it becomes imperative that 

 we should first divide them into groups, com- 

 posed of such genera as are most nearly allied 

 by their structure and general habits, each 

 of which will in turn require our separate 

 notice. 



CLASS. POLYPIFERA. 



Sub-class 1. HYDROZOA. 



Body gelatinous, free, naked, presenting in- 

 ternally a simple stomachal cavity, which is 

 provided at its entrance with highly contrac- 



* See the History of Zoophytology in Dr. John- 

 ston's admirable " History of the British Zoophytes." 

 Lond. 1847. 



