CHAPTER VII 



Dividing Nuclei 



To see the phenomenon as it actually takes place, the blood 

 corpuscles of the newt are favourable objects. 



Newts are kept without food for three months. They are then 

 fed with small worms, cautiously at first. After about ten days 

 there are a large number of young red corpuscles in the blood and 

 in the process of division. These cells are almost devoid of haemo- 

 globin, round and with large nuclei. The complete process takes 

 about half an hour. For further details, see the paper by Jolly 

 (Archives d 1 Anatomic Microscopique, Tome vi. (1904), p. 455). 



The Development of the Frog should be watched. Collect 

 some of the spawn in the spring, placing it in water in shallow 

 dishes. Green weeds should be supplied. Notice the changes, 

 first to the tadpole, then the appearance of legs, the disappearance 

 of the tail, and the attainment of the form of the adult frog. Many 

 details will be noticed and sketches may be made. The very early 

 stages are best observed under a simple lens. 



Ova and Spermatozoa 



The ovary of the frog is most easily made out just after the 

 breeding season, after the full-grown ova have been shed. 



Remove one of the ovaries and place it in 0.7 per cent, saline. 

 Make an incision into it. It contains a cavity. Upon the walls 

 of this cavity are round eminences of various sizes. These are ova 

 in various stages in development. 



Tease out a bit of ovary in 0.7 per cent, saline. Examine with 

 a low power. Note that there are many ova much smaller than 

 those seen with the naked eye. The)- are granular spherical cells, 

 with a clear central part. 



The spermatozoa can be seen by opening one of the testes and 

 pressing out some of its contents upon a slide, mounting in water 

 and examining with a high power. They appear as long motile 

 filaments. More typical spermatozoa can be obtained from the 

 rat, and consist of a small head and a long motile tail. The 



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