1892.] MICROSCOPICAL JOURNAL. 235 



of the Infusoria in the degee of their activivity and especially in 

 their not persisting. The pseudopodia of A. proteus do not 

 persist at all, those of A. radiosa persist for a time but are not 

 permanent. A higher specialization in its molecular structure 

 whereby this pseudopodia ectosarc would be permanent and very 

 active would be a structure comparable with the strong flagellum 

 of the Dino-fiagellata^ as in Noctiluca (Fig. 7), and Peridinium 

 (Fig. 16). 



Amoeba villosa (Fig. 3) is another animal much rarer 

 than A. proteus^ or A. radiosa. Its outline bounded by ectosac is 

 changeable, and even to a slight extent pseudopod-forming, but 

 its motile functions are for the most part confined to certain short 

 and blunt processes, very numerous and located solely at one 

 special part of the body. These give the creature its name. 

 They are apparently a step in the direction of cilia, but with little 

 of the perfection of cilia as they are found in such a creature as 

 Vorticella. In these creatures we have three species of a single 

 genus ; all are somewhat alike, yet all are different ; they are 

 neighboring terms of a series. The same series or genus, Amceda, 

 contains man}^ other species, one of which, A. polypodia, is figured 

 in the act of division in figure four. We shall find that different 

 genera are more unlike than dift'erent species of one genus. 



Difflugia pyriformis inhabits masses of vegetation decaying 

 in fresh water. It is evidently advantageous for protection to be 

 covered with a shell, and Diffiiigia pyriforjnis has a covering 

 made of bits of sand joined together to form a mosaic coat shaped 

 like a flask. This habit is matched among the annelids by Cis- 

 tenides, or among the insects by the larva of the caddis fly, as 

 well as by many other animals. The animal within the shell is 

 an amceba-form being ; its pseudopodia are not, however, gen- 

 eral, but are localized, being placed only at the mouth of the 

 shell — they are in shape like those ol Atnoeba proteus ; and Dif- 

 Jlugia pyrifortnis is such an animal as would result from the 

 habit on the part of many generations oi Amoeba proteus of using 

 a portion of the ectosarc only for ordinary pseudopodial function 

 and protecting the remaining portion by means of a shell. It 

 would not be easy for Dijfflugia with its shell to divide in the 

 same way as Amceba to produce new members, and it is more 

 likely that the act is accomplished by the protoplasm independ- 

 ently of the shell, new shells being subsequently formed. 



Hyalosphenia cuneata (fig. 6). If a shelly covering is ad- 

 vantageous for protection it will seem also advantageous to a 

 creature to be able to produce its own. In Hyalosphenia cuneata 

 we have two deviations from the amoeba structure. There is 

 first an outer shell, which, however, unlike that of /?//^?/^7'a, is a 

 horny or chitinous cuticle formed from a secretion thrown oft' by 

 the ectosarc which hardens on the ectosarc as a mound on coming 

 in contact with the surrounding water. And there are within 

 the cuticle spaces in the protoplasm, " vacuoles," which are filled 



