28 



IXVERTEBKATE ANIMALS. 



As regards the functions of relation, it i§ questionable how far the 

 Anuxba can be said to have distinct perceptions or sensations of any 

 kind. It has no nervous system or organs of sight or hearing, and 

 in all probability it has nothing more than a general sensibility to 

 light. It appears, however, to be fully aware when any object 

 comes in contact with a pseudopodium, and even to have some idea 

 whether this is fit for food. Locomotion, 

 as we have seen, is entirely effected by the 

 temporary processes of sarcode, or pseudo- 

 podia, and there are no permanent organs 

 set aside either for locomotion or for pre- 

 hension — that is, for seizing external 

 objects. 



Many other Ehizopods, more or less 

 closely related to the Amoeba, have been 

 described. Home of these, though resem- 

 bling the Amo?ha in general structure, and 

 in the form of the pseudopodia, have the 

 soft protoplasmic body enclosed in a kind 

 of shell or " test." A good example of 

 these shelled A mcebea is the little Difflugia 

 (fig- '^)) ''• "^ot uncommon iidiabitant of 

 fresh water. In this form the body is 

 enclosed in a sort of shell, composed of 

 sand - grains and other foreign particles 

 cemented together by a kind of horny 

 secretion. The animal can retire within 

 its shell, one end of which is open, so as 

 to allow of the protrusion of the pseudo- 

 podia. In walking, the animal creeps 

 about " head-downwards,'' so to speak — 

 that is to say, with the closed end of the 

 the surface on which it is moving. 



Fig. 7. — Vi^ugla ^vjriformis, 

 greatly enlarged. (Altered 

 fdightly from Carter.) The 

 ca-ie is composed of angular 

 grains of transparent quartz, 

 within which is the transpa- 

 rent outer layer of the Imdy, 

 lined by the finely granular 

 inner layer : n Nucleus ; c c 

 Contractile vesicles. 



shell elevated abovt 



Order III. Foramtnifbra. 



The next order of the Uhizoiioda is that of the Foramimfera, com- 

 prising animals which at first sight appear to be highly complex, but 

 which are really less highly organised than the Amoeba. The Fora- 

 'iiiinifera may be defined as Itlir.opiiihi in whii:Ji the horh/ i.:: protected 

 btf a shell or ''^ test" ; a 'miclcus and contractile vesicle fire wsualli/ 

 present ; and the psci(dopodia are extremely long and thread-like, and 

 interlace with one another so as to form a neticori: 



The most obvious and striking character of the Foraminifera is 



