140 GENERAL HISTOHY OF THE INFUSORIA. 



certainty to its proper place, there is decidedly no reason for excluding it 

 from the animal kingdom. We will not, however, venture to consider the 

 Infusoria furnished with a mouth (Stomatoda, Yon Siebold) as formed, like 

 Polytoma, upon the tj-pe of a simple cell: for, high as we may rate the ad- 

 vantage accruing to science from the comparison of the Protozoa with simple 

 cells, difficulties stand in the way of its complete appHcation in the case of 

 animals of such complicated structure as the Vorticellce for example ; and 

 these cannot be considered as entii^ely done away with until the history of 

 their development has fiu^nished proof that at no period does a fusion of 

 several cells take place. 



" In conclusion, we bring together the results of the investigation as shortly 

 as possible. 



" 1. Polytoma is an animal. 



^'2. It is characterized by a clear investing membrane, which does not 

 consist of cellulose ; two contractile spaces in the substance of the body ; a 

 nucleus with a nucleolus ; two filaments ; and by the deposition of layers of 

 starch-like granules. 



^' 3. The starch-granules may become converted into a blue or green co- 

 louring matter. 



^' 4. Polytoma divides within the investing membrane into two, four, or 

 eight parts, and propagates itself in this manner. 



" 5. It passes into a state of repose." 



These arguments wiU, we fear, not be deemed satisfactory to most natu- 

 ralists. That the investing membrane should not be coloured blue by iodine 

 is an unimportant fact in determining its nature ; for the same thing happens 

 -with many undoubted vegetable tissues, and we are, besides, not sufficiently 

 acquainted "with the chemical history of starch, cellulose, and allied isomeric 

 substances, to appeal to their presence or absence as decisive of an animal or 

 vegetable nature. Then, again, as to the contractile spaces, these cannot be 

 considered peculiar to animal life, seeing that they are present in such gene- 

 rally recognized vegetable forms as Chlamydomonas, Gonimn, and Volvooc. 



Moreover, Schneider himself describes starch -granules and chlorophyll- 

 vesicles within Polytoma, which, if these substances had any decisive bearing 

 on the question, would quite settle its affinity with plants, irrespective of the 

 constitution of the enveloping membrane. Besides, the whole history of the 

 organism accords so closely with the known phenomena of life and develop- 

 ment of the simplest plants, that this alone must cany much weight in fixing 

 its position in the scale of beings. 



FAMILY II.— CRYPTOMOI^ADINA. 



(Plates XYIII. 29—34.) 



The Crtptomonadina, which follow the Monadina in the arrangement of 

 Ehrenberg, claim but a brief consideration, inasmuch as so little precise infor- 

 mation is obtainable with respect to them, and as the existence of possibly 

 all of them as independent organisms is a matter of much uncertainty. The 

 genera enumerated were — Cryptomonas, Ojphkloinonas, Urocentrum, Lagenella, 

 Cryptoglena, and TracJielomonas. To characterize the Cryptomonadina in two 

 words, they are encysted Monadina or Eugienese. Ehrenberg puts forward the 

 following account : — '' They exhibit all the characteristics of the Monadina, 

 but have, in addition, an external diaphanous membrane or lorica, which 

 either encloses them entirely—?', e. forms an urceolus, — or leaves one side 

 exposed, and so constitutes merely a shield — scutellum. Locomotive organs, 

 in the shape of two delicate filiform and generally retractile filaments or pro- 



