28 



ZOOLOGY 



SECT. 



the corpuscles disseminated through a liquid plasma, which 

 takes the place of the ground substance of the connective tissues. 



FK-. is. Nerve cells. A. niultipolar; 

 , bipolar. 



]"].. I.'. Xcrve fibre.-. A. iiicilnlluted ; 

 B, npn-medullated ; ax, n. ., 

 ii .'. medullary sheath : 

 neurilemma. 



In a large proportion of cases such corpuscles are similar to 

 Amcebae in their form and movements ("/nt.i/i/</ corpuscles, 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 arc able like 

 Amcebse 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 plasm mHi'm. 



The characteristic cells of the 

 reproductive tissues are the ova 

 and the spermatozoa or sperms. The 

 ova (Fig. 4\ when fully formed, are 

 relatively large, usually spherical 

 cells, sometimes composed entirely 

 of protoplasm, sometimes with an 

 addition of mitri-ent food-yolk. Each 

 ovum, as already mentioned, en- 

 closes a large nucleus (//. / -m-iiinl 

 c< *i<-]<) and in the interior of that 

 one or more nucleoli or germinal 

 spots. The sperms (Fig. 20) are 

 extremely minute bodies, nearly 



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

 one extremity, and commonly with a rounded lu:ad at the other. 



KH.. 20. Various forms of si>crmato/,,;i. 

 (i. i >f a Mammal ; l>. of a Turbullariaii 

 worm ; c, and -'.and e, of Xematode 

 worms; /, of a Crustacean; <i. of a 

 Salamander; A, the commonest form 

 with oval head and long- flagellurn. 

 (From Lang's Comparativi Anatomy.) 



