90 ZOOLOGY SECT. 



ORDER 4. MYXOSPORIDEA. 



This group includes a small number of genera which are amoeboid in the 

 trophozoite phase, and which reproduce continuously by spore-formation 

 during that phase (Fig. 68, A). Many nuclei are present in the amoeboid 

 body, which may be of comparatively large size. The spores (B) produced 

 within the protoplasm of the trophozoite are provided each with one or more 

 bodies like the nematocysts of zoophytes and jelly-fish. [See Section IV.] 

 Myxosporidea occur as parasites mainly of fishes and amphibians, but very 

 many occur in various groups of Invertebrates. '* Pebrine," the destructive 

 silk-worm disease, is due to the presence of a Sporozoan belonging to this 

 order. A good example of the order is Myxidium, found in the urinary bladder 

 of the pike. 



ORDER 5. SARCOCYSTIDEA. 



The best-known form of this order is Sarcocystis (Fig. 69), which occurs in 

 the flesh of mammals, each parasite having the form of a long spindle embedded 



Fia. 69. Sarcocystis miescheri, adult form (s) in striped muscle of pig. (From 

 Biitschli's Protozoa, after Rainey.) 



in a striped muscular fibre. They are often known as Rainey's or Miesclier's 

 corpuscles. The protoplasm divides into spores from which falciform young 

 are liberated. 



CLASS V. INFUSORIA. 



1. EXAMPLE OF THE CLASS Paramoecium caudatum. 



Structure. Paramoecium, the " slipper-animalcule," is tolerably 

 common in stagnant ponds, organic infusions, &c. The body 

 (Fig. 70) is about ] mm. in length, somewhat cylindrical, but 

 flattened, with distinct upper and lower or dorsal and ventral 

 surfaces, and anterior and posterior ends, the latter rather more 

 pointed than the former. On the ventral face is a large oblique 

 depression, the buccal groove (hue. gr.), leading into a short gullet 

 (gul.), which, as in Euglena, ends in the soft internal protoplasm. 



The body is covered with small cilia arranged in longitudinal 

 rows and continued down the gullet. The protoplasm is very 

 clearly differentiated into a comparatively dense cortex (cort.) and 

 a semi-fluid medulla (med.), and is covered externally by a thin 

 pellicle or cuticle (cu.) which is continued down the gullet. Each 

 of the cilia is connected at its base with a very small basal granule 

 (rendered visible only by special staining of fixed specimens) situated 

 below the pellicle. 



In the cortex are found two nuclei, the relations of which are 

 very characteristic. One, distinguished as the meganucleus (nu.), 



