306 GENERAL BIOLOGY 



most serviceable) should study the sections, identifying 

 successive division phases, and should sketch at least the 

 spireme, splitting chromosomes and a complete spindle with 

 the chromosome complex upon it. 



Newly laid eggs of pond snails will show the formation of 

 the polar bodies (in external aspect ; not chromosome con- 

 tent), and as these persist to the 8-cell stage or later they 

 may be found and sketched in outline in relative proportion 

 to the egg to which they are attached. 



The record of this study may consist of notes and sketches 

 of the principal things observed. 



Study 38. Observations on parthenogenesis* 



Materials needed: Growing plants of cabbage, turnips 

 or lettuce (or any other green house plant that may be more 

 convenient), infested with viviparous parthenogenetic 

 female aphids; also, small individual plants Tgrowing 

 in thumb pots, and covers for them (see appendix) . 



The student should isolate a newly born, (or, at least, a 

 very young) aphid, transferring it (to avoid injury) on the 

 point of small camel's hair brush to an uninfested lettuce 

 plant in thumb pot, and covering it as in a cage. He should 

 keep the plant growing and watch the reproduction of the 

 aphid from time to time, recording progress at each observa- 

 tion. 



Continue through the lifetime of a single individual at 

 least, so that data may be available for calculating possible 

 progeny and rate of increase for a season. Note recurrence 

 of birth of young, and total absence of males during the 

 experiment. Add to your record of this experiment at each 

 time of observation ; trust nothing to memory. After the 



*This is a running experiment, covering a number of weeks at 

 least, _but it will require only a few moments observation each week 

 after it is started. 



