228 



THE RISE OF ANIMAL LIFE 



9ciGp05»Tinqeqq5 



Fig. 11-23. Grasshopper depositing its eggs, and the 

 larvae hatching some time later. 



is somewhat better developed than that 

 of the crayfish, as is indicated in both its 

 structure and function. 



Excretorij system. The excretory organs, 

 the Malpighian tubules, have already been 

 mentioned in connection v^ith the digestive 

 tract. Insects are the only animals whose 

 excretory glands (kidneys) open directly 

 into the intestine (Fig. 11-21). The long, 

 coiled tubules lying in the haemocoel are 

 bathed in blood so that suspended nitrog- 

 enous wastes are easily removed. Uric acid 

 has been found to be the end product of 

 nitrogenous metabolism in insects. 



Reproductive system. On late August 

 days it is common to see grasshoppers cop- 

 ulating. Some days after fertilization tlie 

 female grasshopper lays her eggs (Fig. 

 11-23). She uses her powerful pointed ovi- 

 positors for digging a hole in the soil where 

 the eggs are deposited, together with a 

 mucous substance which cements them into 

 a packette, known as a pod. She lays about 

 20 eggs at a time, and may deposit as 

 many as ten pods before death overtakes 

 her some days after the egg laying is ac- 

 complished. The eggs begin to develop as 

 soon as they are laid and become well- 

 formed embryos before cold weather sets 

 in. The embryos then undergo a rest period, 

 the diapause, in which they pass the winter. 

 In the warm spring days, development is 

 resumed and the embryos hatch in early 

 summer as nymphs (Fig. 11-23), which re- 

 semble the adult grasshopper without 

 wings. Nymphs undergo several molts dur- 

 ing their subsequent rapid growth, the 



wings appearing and becoming longer at 

 each shedding period. It is during this 

 period of rapid growth, when their bodies 

 demand so much food, that the animals are 

 so destructive to crops. The summer is 

 spent leisurely, feeding and growing, until 

 the breeding season begins. 



The sex organs of the grasshopper consist 

 of a pair of testes and ovaries (Fig. 11-21). 

 The testes are made up of several small 

 tubules or follicles, which are joined to the 

 seminal vesicle by means of the vas defe- 

 rens; the latter then join to the ejaculatory 

 duct and copulatory organ, the penis. A 

 pair of accessory glands secrete a fluid in 

 which the sperms are suspended. The large 

 ovaries are composed of several egg tubes 

 in which the eggs develop; two oviducts ex- 

 tend from the ovaries and join to form the 

 vagina. A pair of accessory glands is also 

 present in the female, which contributes to 

 the eggs during their formation. 



The honeybee 



The honeybee has been associated with 

 man as a domestic animal for many thou- 

 sands of years and stories about this ani- 

 mal have found their way into the writings 

 of poets and historians as well as natural- 

 ists from very early times. Aristotle de- 

 scribed the parthenogenetic development 

 of the drone bee, even though he had no 

 microscope witli which to verify his state- 

 ments. The bee offers excellent material 

 for the study of social behavior in lower 

 animals and is a remarkable illustration of 

 adaptation. The more scientists study the 

 social life of this little animal, the more 

 remarkable does it appear. 



Bees have learned to live in colonies 

 where all members work for the community 

 in a rigid caste system. There is one queen 

 which lays all of the eggs for the colony, 

 a number of drones (males), one of which 

 fertilizes each newborn queen, and thou- 

 sands of sterile females, called workers, 

 which do all the work of the colony (Fig. 



