LIFE HISTORIES OF THE PROTOZOA. 
BY A. S. PACKARD, JR. 
_ Tue design of the present series of papers is to give the results 
of studies by different authors on the development of the typical 
forms of animals, beginning with the lowest and ending with man. 
I. THE MONERA. 
Structure and Habits. Hæckel, in 1868, applied to this group 
of organisms, which are doubtfully referred to the animal kingdom, 
the term Monera (from povjpns, simple) in allusion to the extreme 
simplicity of their structure. ‘Their whole body,” he remarks, 
‘in a fully developed and freely moving condition, consists of an 
entirely homogeneous and structureless substance, a living parti- 
cle of albumen, capable of nourishment and reproduction.” They 
differ from the Amcebx, hitherto supposed to be as simple as any 
organism, in the want of a nucleus and of contractile vesicles. 
Moreover, they (as in Protameeba) differ from the Rhiz d 
Ameba in being entirely homogeneous in structure, there being, 
as Heckel observes, “no apparent difference between a morè 
tenacious outer and a softer inner sarcode mass,” as is “ percep- 
tible in most, perhaps in all, true Amæbæ.” 
The motions of these Moners are effected by contraction of the 
homogeneous substance of the body, and by the irregular protru- - 
sion of portions of the body, forming either simple processes 
(pseudopodia) or a net-work of gelatinous threads. The food is 
ZAR in after the manner of the Ameeba, the diatom, desmid oF 
me protozoan being surrounded by the pseudopodia an igi 
aiden by the extremely extensible body mass. Haeckel says = 
reproduction is effected solely in a non-sexual manner. per : 
but not always, the freely moving condition alternates with ak . 
of rest, during which the body surrounds itself with an °X . 
structureless covering,” becoming in fact encysted. 
he Monera are divided into two groups: 
1. G@ymnomonera, comprising the genera Bathybius, 
bius, Protameba, Protogenes and Myzxodictywm, which d 
come encysted and consequently protected by a case. 
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