4 GEKEP.AL HISTOIiT OF 



Again, in the gemif! Bodo, some of the ppociee arc proper Entozoa. 

 and, tlicrcfore, ought to be exchided. Having, however, taken that 

 work as the basis of my arrangement, all the species described 

 therein will be found here. 



With regard to the Spermatozoa of animals, our laiowledgo of 

 them is but scanty and confused, arising principally from their 

 extreme minuteness, which, even ■s\'ith the assistance of our most 

 perfect microscopes, places them at the very limit of our vision. 

 The great importance of this subject, especially to the medical pro- 

 fessor, has obtained for it, from several distinguished naturalists, 

 long and laborious researches ; but, on the whole, the results have 

 been conti'adictorj- (see section XTII.) It will be sufficient, therefore, 

 to say, that since the time of their disco veiy (1676), up to the 

 present period, all that we know of the true Spermatozoa of animals, 

 is, that they are not distinguishable from Cercaria, found in the livtr 

 of snails, the animal organization of which has been made out by 

 Bauer, AYagner, and Elu-cnbcrg. 



The recent discoveries of Dr. Enger on the Spermatozoa of plants 

 is a subject of such deep interest, and so little known in this 

 country, that I have introduced a description of them under the 

 genus Spirillmn ; while original di^awings of them will be found in 

 Plate XII. 



It has been said that the line of demarcation between many 

 species of animals and plants — the transition from the one kingdom 

 to the other — is not easily defined. Indeed, so close is the connec- 

 tion between them, that some members of the families Clostei-ina, 

 Vibrionia, and Bacillaiia, which are considered by Ehrcnberg to bo 

 animals, are, by many eminent botanists, set down as belonging to 

 the vegetable kingdom, and classed with the minute aquatic alga; of 

 the genera Oscillatoria, Spyrogj-ra, &.c. The true species of the 

 two genera just named, it must be admitted, are not of animal 

 structure ; and Dr. Ehrcnberg has given us the following reasons 

 ■why they are not included with the lafusoria : — 1 . They have no 

 oral apertm-e. 2. They never propagate by direct self-di\-ision, but 

 by the mere dissolution of the gemmrc. 3. They increase in size 

 only by the growth of the gemmae. 4. They have both the external 

 and internal rigidity of vcgetablo organization. 5. The impregna- 



