760 MICROSCOPIC FORMS OF ANIMAL LIFE 



its envelope entire ; and by a repetition of the process, as many as 

 sixteen segments, each attaining the likeness of the parent, are seen 

 thus inclosed, their flagella protruding through the general invest- 

 ment. This compound state being supposed by Ehrenberg to be the 

 normal one, he named it accordingly. But the parent-cyst soon 

 bursts, and sets free the contained ' macro-spores,' which swim about 

 freely, and soon attain the size of the parent. Again, the posterior 

 part of the body of certain individuals shows an accumulation of 

 granular protoplasm, giving to that region a roughened acorn -cup- 

 like aspect ; the bursting of the projection, while the creature is 

 actively swimming through the water, sets free a multitude of 

 indefinitely shaped granular fragments, within each of which a 

 minute bacterium-like corpuscle is developed ; and this, on its 

 release, acquires in a few hours the size and form of the original 

 monad. This process seems analogous to the development of ' micro- 

 spores ' among protophytes by the direct breaking up of the proto 

 plasm. It is, like the previous process, non-sexual or yoii-idial, the 

 true generative process consisting here, as in the preceding cases, in 

 the 'conjugation' of two individuals, with the usual results. 



The hooked monad (Heteromita uncinata, Kent) is another bi- 

 flagellate form, usually ovate \vith one end pointed, and from 3- ( j\ M ,th 

 to ^o oth of an inch in length, being distinguished from the pre- 

 ceding by the peculiar character of its flagella, of which the one that 

 projects forwards is not more than half the length of the body, and 

 is permanently hooked, while the other, whose length is about twice 

 that of the body, is directed backwards, flowing in graceful curves. 

 Its motion consists of a succession of springs or jerks rapidly follow- 

 ing each other, which seems produced by the action of the hooked 

 flagellum. Multiplication takes place by transverse fission, and con- 

 tinues uninterruptedly for several days. A difference then becomes 

 perceptible between larger and smaller individuals, the former being 

 further distinguished by the presence of what seems to be a con- 

 tractile vesicle in the anterior part of the body. Conjugation occurs 

 between one of the larger and one of the smaller forms, the latter 

 being, as it were, absorbed into the body of the larger ; and the 

 resulting product is a spherical cyst, which soon begins to exhibit 

 a cleavage -process in its interior. This continues until the whole 

 of its sarcodic substance is subdivided into minute oval particles, 

 which are set free by the rupture of the cyst, and of which each is 

 usually furnished w^ith a single flagellum, by whose lashing move- 

 ment it swims freely. These germs speedily attain the size and form 

 of the parent, and then begin to multiply by transverse fission, thus 

 completing the ' genetic ' cycle. 



The calycine monad of the same observers (Tetramitits rostratus, 

 Perty) has a length of from 9 ^th to y^^th of an inch, and a com- 

 pressed body tapering backwards to a point. Its four flagella (which 

 constitute its generic distinction) arise nearly together from the 

 flattened front of the body, and its swimming movement is a grace- 

 ful gliding. Near the base of the flagella are a pair of contractile 

 vesicles, and further behind is a large nucleus. Multiplication takes 

 place by longitudinal fission, which is preceded by a change to a semi- 



