TWELFTH WEEK. 



The work of this and the following weeks is to be selected from 

 the work laid down as elective work in this manual. If work in phys- 

 iology or morphology is elected all five weeks must be devoted to a sin- 

 gle group in one of these subjects. Other work may be taken in any 

 combination of one-week units. The directions for elective work will 

 be found as follows: 



Description under week seven; 



Determination under week eight; 



Life history under week twelve; 



Field work under week thirteen; 



Physiology under weeks nine to eleven; 



Morphology under weeks fourteen to sixteen. 



ELECTIVE WORK. Life History. 



The laboratory work of weeks twelve to sixteen may be repre- 

 sented by investigations upon the life histories of insects. From the 

 nature of this work it cannot generally all be done during these weeks, 

 but should be begun earlier. Three transformations will be considered 

 equivalent to a week's work. Each stage should be represented by a 

 short descriptive note or sketch and by a properly mounted specimen. 

 Thus four stages of one insect would represent a week's work, as 

 would two stages of each of three insects. Parasites will be counted 

 as though they were stages of the insect studied. 



Eggs may be hatched by placing them in a dry vial, stoppered and 

 labeled, or they may be at once placed in breeding cages, as described 

 below. 



Larvae and nymphs, if vegetable feeders, may be kept in a breeding 

 cage made as follows: A twig of the food plant is placed in a flowerpot 

 filled with moist sand and covered by a lantern or lamp globe which is 

 closed above with a piece of cloth tied on. If the larvae are young it 

 may be necessary to renew the food from time to time. Another 

 method is to enclose the insect in a cheese-cloth sleeve tied over the 

 twig upon which it feeds. A third way is to watch the insect as it oc- 

 curs in nature, being very careful that there is no mistake in identity. 

 Carnivorous forms must be supplied with their appropriate food, but 

 practically the same method may be used. 



Pupae are best kept in tight boxes, which should be of a size suffi- 

 cient to allow the full expansion of the wings. 



Adults can often be made to lay their eggs, sometimes by simply 

 confining the females in a box; generally, however, it is best to confine 

 her in a breeding cage with the appropriate food for her young. 



