II 



PHYLUM PROTOZOA 101 



stalk of Vorticdla. Infusors and other organisms are caught by 

 the tentacles (4, 0), the cuticle of the prey is pierced or dissolved 

 where the sucker touches it, and the semi-fluid protoplasm can 

 then be seen flowing down the tentacle into the body of the 

 captor, A single tentacle only may be present (3), or the tentacle 

 may be branched (4), the extremity of each branch being suc- 

 torial. In some forms there are no terminal suckers (5), and the 

 tentacles are waved about to catch the prey instead of standing 

 out stiffly as in Acineta. In other cases there are one or more 

 long, striated tentacles with tufted ends (7). 



The nucleus may be ovoid (/a), horseshoe-shaped, or branched 

 (8, 9) : in many cases a micronucleus (1 a, mi. nu.) has been found 

 and it probably occurs in all. There are one or more contractile 

 vacuoles (c. vac.). 



Some genera are naked (1) : others form a stalked shell or 

 lorica (a) like that met with in many of the Mastigophora. 



The only colonial form is the wonderful Dendrosoma (9), in 

 which the entire colony attains a length of about 2 mm., and bears 

 an extraordinary resemblance to a zoophyte (vide Sect. IV.). It 

 consists of a creeping stem from which vertical branches spring, 

 and the various ramifications of these are terminated in Podo- 

 phrya-like zooids with suctorial tentacles. The nucleus is very 

 remarkable, extending as a branched axis throughout the colony 

 (b, nu.). Micron uclei of the ordinary character are present 

 as well. 



Reproduction by Unary fission takes place in many species. 

 In Ephclota gemmipara (S) a peculiar process of budding occurs : 

 the distal end of the organism grows out into a number of 

 projections or buds, into which branches of the nucleus extend. 

 These become detached, acquire cilia on one surface, and swim 

 off (b). After a short active existence tentacles appear and the 

 cilia are lost. In this case budding is external, but in Acineta 

 tnberosa (2b) the buds become sunk in a depression, which is finally 

 converted into a closed brood-cavity (b.c.) : in this the buds take on 

 the form of ciliated embryos, which finally escape from the parent. 

 In Dendrosoma the common stem of the colony produces internal 

 buds (b, Id.). 



Further Remarks on the Protozoa. 



The majority of the Protozoa are aquatic, the phylum being 

 equally well represented in fresh and salt water. They occur 

 practically at all heights and depths, from 8,OOQ v to 10,000 feet 

 abovejsea-level, to a depth of from 2,000 to 3,000 fathoms. Some 

 forms, such as species of Amoeba and Groin ia, live in damp sand 

 and moss, and may therefore be almost considered as terrestrial 

 organisms. In accordance with their small size and the readiness 

 with which they are transported from place to place a large pro- 



