! NKOSPORIDIA 67 



\\'ithin these there are formed enormous numbers of crescent-shaped 

 spores. 



These threads or tubes (" Miescher's tubes ") are distinctly visible 

 to the naked eye, and are common in butcher-meat. Sheep and I 

 are nearly always more or less infected, the parasites being particularly 

 frequent in the muscular wall of the alimentary canal especially the 

 oesophagus. A virulent toxin is commonly formed in the substance of 

 the parasite but it is only in exceptional cases, as in the species found 

 in the Mouse, that marked pathological symptoms are produced. 



Nothing is known definitely as to the normal means of transmission 

 though mice can be infected experimentally by feeding them on infected 

 muscle. The fact that spores sometimes possibly by bursting of the 

 cyst find their way into the circulating blood indicates at least the 

 possibility of there being a blood -sucking intermediate host. 



(6) HAPLOSPORIDIA. In this group are included a number of com- 

 paratively simple but still very insufficiently known parasites. They 

 typically begin their existence as an amoebula which may reproduce 

 repeatedly by fission but which eventually increases greatly in size, 

 becomes multinucleate, and breaks up into numerous spores. These 

 spores are simple in structure and are without the polar capsules which 

 are so characteristic of the Cnidosporidia. 



Some cause disease, sometimes very destructive epidemics, in Fish ; 

 one is found in a rare type of tumour of the nose in Man (Rhinosporidium), 

 while others live within the bodies of various kinds of animals without 

 producing any obvious pathological disturbance. 



IV. CILIATA 



The last great division of the Protozoa the CILIATA or INFUSORIA 

 includes a vast assemblage of species showing wonderful variety in form 

 and in the details of their structure. Included amongst them are the 

 most complex and highly organized of all the Protozoa : some indeed 

 being unicellular may be said to be the most complicated and highly 

 organized individual cells known. We shall commence their study by 

 considering in detail a very common member of the group, Paramecium, 

 specimens of which are commonly to be seen in the form of minute white 

 specks, just visible to the naked eye, gliding slowly about in fresh water in 

 the neighbourhood of decaying organic matter. 



Observed under the microscope a Paramecium is seen to have the 

 form shown in Fig. 28. The body is limited by ectoplasm of remarkable 

 complexity in which four layers can be distinguished. The outermost 



FI 



