28 



ZOOLOGY 



SECT. 



itlr 



the corpuscles disseminatBP through a liquid plasma, which 

 takes the place of the ground substance ofthe connective tissues. 



med 

 i f 



I IB 



Fi<;. 18. Nerve cells. A, multip >>ir ; 

 B, bipolar. 



Fie. I 1 .'. Nerve fibres. J, medullated 

 B, non-niedullated ; a.r, iie\iraxis 

 med, medullary sheath; neur. 

 neurilemma. 



In a large proportion of cases such corpuscles are. similar to 

 Amoebae in their form and movements (ii'inu'loitJ eurpu^ies, leuco- 

 cytes). In the blood of Vertebrates leucocytes occur along with 

 coloured corpuscles of definite shape containing the red-colouring 

 matter (hccmoglobin) of the blood. The leucocytes are able like 

 Amoebae to ingest solid particles, and under certain conditions a 



number of them may unite to- 

 gether to form a single mass of 

 protoplasm, with many nuclei,, 

 termed .a plosmodium. 



The characteristic cells of the 

 reproductive tissues are the ova 

 and the spermatozoa or $j>ci'i/is. The 

 ova (Fig. 4\ when fully formed, are 

 relatively large, usually spherical 

 cells, sometimes composed entirely 

 of protoplasm, sometimes with an 

 addition of nutrient fooil-yolk. Eacl 

 ovum, as already mentioned, ei 

 closes a large- nucleus (gernyim 

 vesicle) and in the interior of tht 

 one or more nucleoli or germii 

 _ spots. The sperms (Fig. 20) 



extremely minute bodies, nearl 



always motile, usually slender and whip-like, tapering towai 

 extremity, and commonly with a rounded head at the other. 



Fii. 'Jo. Various forms of spcTmato/na. 



K. of a Mammal; l>, of :i Turbellarian 



00 ; C, and i/, and ., of Nc-niatodu 



QB ; .'', of a ( 'nistarcan ; <i. of ;i 



Salamander; //,tlie commonest form 



with >val head and lun^ tlayellum. 

 (Fr.au Land's Comparative Anatomy.) 



