744 MICROSCOPIC FORMS OF ANIMAL LIFE PROTOZOA 



into contact they scarcely sho\v any disposition even to mutual 

 cohesion, still less to fusion of their substance. Sometimes the 

 protrusion seems to be formed by the ectosarc alone, but more 

 commonly endosarc also extends into it. and an active current of 

 granules may be seen to pass from what was previously the centre 

 of the body into the protruded portion, when the latter is undergoing 

 rapid elongation ; whilst a like current may set towards the centre 

 of the body from some other protrusion which is being withdrawn 

 into it. It is in this manner that an Amoeba moves from place to 

 place, a protrusion like the finger of a glove being first formed, into 

 which the substance of the body itself is gradually transferred, and 

 another protrusion being put forth, either in the same or in some 

 different direction, so soon as this transference has been accom- 

 plished, or even before it is complete. The kind of progression thus 

 executed by an Amoeba is described by most observers as a ' rolling ' 

 movement, this being certainly- the aspect which it commonly 

 seems to present ; but it is maintained by MM. Olaparede and 

 Lachmann that the appearance of rolling is an optical illusion, 

 since the nucleus and contractile vesicle always maintain the same 

 position relatively to the rest of the body, and that ' creeping ' would 

 be a truer description of the mode of progression. It is in the 

 course of this movement from place to place that the Amoeba en- 

 counters particles which are fitted to afford it nourishment ; and it 

 appeal's to receive such particles into its interior through any part 

 of the ectosarc, whether of the body itself or of any of its lobose 

 expansions, insoluble particles which resist the digestive process 

 being got rid of in the like primitive fashion. 



It may often be seen that portions of the sarcode-body of an 

 Amoeba, detached from the rest, can maintain an independent exist- 

 ence ; and it is probable that such separation of fragments is a,ii 

 ordinary mode of increase in this group. When a pseudopodial lobe 

 lias been put forth to a considerable length, and has become en- 

 larged and fixed at its extremity, the subsequent contraction of the 

 connecting portion, instead of either drawing the body towards the 

 fixed point, or retracting the lobe into the body, causes the connect- 

 ing band to thin away until it separates ; and the detached portion 

 speedily shoots out pseudopodial processes of its own, and comports 

 itself in all respects as an independent Amosba. Multiplication 

 also takes place by regular binary subdivision. Various observer's 

 have seen phenomena which they have supposed to be evidence of the 

 formation of ' swarm-spores ' * or of the development of cysts, but it 

 must be borne in mind that a large number of protozoa pass during 

 the course of their life through amoebiform stages, some of which 

 may have been taken as true species of Amoeba. No sexual act has 

 been certainly recognised as part of the life-history of Amoeba, the 

 union of two or more individuals, which may be occasionally wit- 

 nessed, having more the character of the ' zygosis ' of Actinophiys. 

 A sarcodic organism discovered by (ireef, and named by him 

 Pel&myxa palustris (fig. 578), which spreads over the bottom of 

 stagnant ponds in the condition of sliniy masses of indefinite form, 

 1 Prof. A. M. Edwards (U.S.A.) in Monthly Microbe. Joi/ni. vol. viii.1872, p. 29. 



