PROTOZOA 



the Cambrian. The older forms are simple Sphaerellaria and 

 Nassellaria. From a synopsis of the history of the order in 

 Haeckel's Monograph (pp. clxxxvi.-elxxxviii.) we learn that while 

 a large number of skeletal forms had been described by Ehren- 

 berg, Huxley in 1851 published the first account of the living 

 animal. Since then our knowledge has been extended by the 

 labours of Haeckel, Cienkowsky, E. Hertwig, Karl Brandt, and 

 A. Borgert. 



5. Peoteomyxa 



Sarcodina without a clear ectoplasm, ivhose active forms are 

 amoeboid or flagellate, or pass from the latter form to the former ; 

 multiplying chiefly, if not exclusively , hy Irood-formation in a 

 cyst. No complete cell -pairing {syngamy) known, though the 

 cytoplasms may unite into plasmodia ; pseudopodia of the amoeboid 

 forms usually radiate or filose, hut without axial filaments. Sapro- 

 phytic or parasitic in living animals or plants. 



This group is a sort of lumber-room for forms which it is 

 hard to place under Ehizopoda or Flagellata, and which produce 

 simple cysts for reproduction, not fructifications like the Mycetozoa. 

 Tlie cyst may be formed for protection under drought (" hypno- 

 cyst"), or as a preliminary to spore -formation (" sporocyst "). 

 The latter may have a simple wall (simple sporocyst), or else 

 two or three formed in succession (" resting cyst "), so as to en- 

 able it to resist prolonged desiccation, etc. : both differing from the 

 hypnocyst in that their contents undergo brood formation. On 

 encystment any indigestible food materials are extruded into the 

 cyst, and in the " resting cysts," which are usually of at least 

 two layers, this faecal mass lies in the space between them. The 

 brood-cells escape, either as flagellate- cells, resembling the simpler 

 Protomastigina, called " flagellulae," and which often become 

 amoeboid (Fig. 29); or already furnished with pseudopodia, and 

 called " amoebulae," though they usually recall Actinuphrys rather 

 than Amoeba. In Vampyrella and some others the amoebulae 

 fuse, and so attain a greater size, which is most probably advanta- 

 geous for feeding purposes. But usually it is as a uninucleate 

 cell that the being encysts. They may feed either by ingestion 

 by the pseudopodia, by the whole surface contained in a living 

 host-cell, or by passing a pseudopodium into a host-cell 

 (Fig. 29 5). They may be divided as follows : — 



