9 



IXVEHTEP.liATE ANIMALS. 



aiice of a single cell, consisting of an ill-defined membranous envel- 

 ope, filleil with a more or less gramdar sarcode containing fatty 

 granides, and liaving in it a little central bladder or vesicle — the 

 "nucleus" — which in turn encloses a solid particle or " nucleolus " 

 fig. 4, a and h). The outer covering or cuticle with which the 



Fig. 4.— :>[orplinlof;y and develnpinent r.f r/rc.y riiiiih' (after Sti'in and Lielicrkiilin), 

 a St'ilorlniUL-hus oUgacanlhiis, a " itiryslidiaii " (iiegarinr ; b Grej^ai'ine of the 

 eartli-^\nriii ("iiioiiocystidt'an ■'); c Tlie sairie encysted; (/ Furtlier stage of tlie 



same, \\itli II rmtents di\idcd into " pseinlnnaviccllie-" ; e Free "pseudonavi- 



eelke": / At Itil'nTaa mass iif in-otnplasni lilterateil from a iiseudonavicella ; 



17 and /( Aethe funus nf /. .\ll tlie Mglirrs are i,'reatly enlarged. 



protoplasmic body is enclnseil may be quite .smooth, or it maybe 

 f\innshe<l with bristles or sjiines, and in .some cases even cilia have 

 been observed. Beyond the nucleus an<l nucleolus no definite 

 organs have been <letected in tlie (>'r('(/(fr//((f' ,• and all the piroces.ses 

 of assimilating fnod and getting rid of waste or injurious ])roducts 

 mu.st be eti'ected liytln' general siirf.-ice nf the body. As we shall 

 see, however, this is connnnn in internal jiarasites, which are not 

 jiecessit.-ited to live ujion solid f<iod, but which are enabled to subsist 

 simjily 1>}' indjibing the nutritive juices of their hosts. 



Tile following is a Liief ondine of Ibe jirneess of reproihietion, as it lias Vieen 

 oliserved in the t'/r'/Dri'ii', sonieliines in a single in<liviilual, soiiietinies in two 

 imlividnals ■i\liirli lia\e eoine t<igellier and completely coaleseod and ineltetl 

 into one aiiollicr. Tlie (in'tjfi n int lieeniiies eniniiletely niotion!es.s, assiune.s a 

 gloliulai- form, ami ilevt'loiri I'oiiml itself ii tliirk siriictnreles.s coat or eiiveloiie, 



