Subkingdom I. PROTOZOA. 



ACRITA. AMOEPHOZOA. SARCODEA. PLASTIDOZOA. 

 HYPOZOA. 



Minute, nearly structureless animals, composed of a gelatinous 

 matter [protoplasm or sarcode], and not developing true layers. 

 Eeproduction principally by fission, or by the breaking up of the 

 nucleus. 



The Protozoa differ from the rest of the animal kingdom in 

 that they present no structural elements, or, even if they possess 

 distinct cells, these cells do not develop into tissues. Such tissues 

 as may be found in the higher Inftfsoria originate, not from the 

 cells, but by changes in the physical and chemical characters. It 

 is, however, undecided whether all Protozoa are unicellular. 



In Monera there is no nucleus ; and it has only been recently 

 recognized in some of the Foraminifera. In all other Protozoa 

 there is a nucleus [ = endoplast, Huxley]. 



In the absence of a nervous system, and in its inherent self- 

 acting power, Bowerbank suggests the hypothesis that the sarcode 

 may be a diffused form of nervous matter. * 



One mode of reproduction is by conjugation (zygosis), Two 

 bodies come together, and a fusion more or less complete takes place. 

 After a time the nucleus breaks up into a number of spores, or 

 the spores are emitted in clouds without any apparent rupture of 

 the surface. 



Bathybius, supposed to have been a living protoplasmic sub- 

 stance, is now known to be " little more than sulphate of lime 

 precipitated in a flocculent state by strong alcohol." 



The classification and even the limits of the Protozoa are still 

 contested ; and the descriptions of these organisms are " in many 

 instances very contradictory." It is doubtful whether many of 

 them can be regarded as any thing more than stages in the develop- 

 ment of other animals or of plants. Glaus (1876) has two classes 

 Rhizopoda and Infusoria treating the remainder as outside 

 the animal kingdom, and more related to Algse and Fungi. 

 These are Schizomycetes (Bacteria), Myxomycetes (Trichia, 

 MChalium) ; Flagellata (Monas, Volvox, Euglena, Peridium, Noc- 

 tiluca) ; Catallacta (Magosph&rci) ; Labyrinthulese, apparently 

 related to the Diatomaceae ; and Gregarinida. Schmarda (1877) 

 has five classes Ehizopoda, restricted to Amceboidea, Acinetidse, 



