OTHER INSECTS 163 



skeleton. The remaining mass, in which three pairs of ganglia are 

 fused, constitutes the so-called brain, which lies dorsally in the front of 

 the head close to the bases of the antennse and sends large nerves to 

 the compound eyes and smaller ones to ocelli and antennae. A pair of 

 circumesophageal connectives extends from the brain to the ventral 

 nerve cord. Of the ventral ganglionic masses, five are in the abdomen, 

 three in the thorax, and one in the head. The one in the head is 

 termed the subesophageal ganglion. In the anterior part of the thorax 

 the nerve cords pass under a part of the exoskeleton, the tentorium. 

 Carefully insert the point of the scissors and cut the tentorium on 

 each side so that it can be removed and thus expose the subesophageal 

 ganglion. The connectives between it and the brain, and between it 

 and the first thoracic ganglion, can now be found. Such a nervous 

 system is characteristic of the entire Phylum Arthropoda, and also of 

 the Phylum Annelida. Compare in position and structure with the 

 nervous system in the frog and man. Draw the nervous system from 

 a dorsal view (X 4), including a simple outline of the body and 

 placing each ganglion in its proper somite. Note the position of the 

 esophagus as it is now exposed and add to the drawing called for in 

 paragraph (f). 



III. REPRODUCTION AND DEVELOPMENT 



Exercise 10. — Eggs and Juvenile Stages. 



(a) The spermatozoa are transferred from the male to the female 

 during sexual union and retained in a seminal receptacle where they 

 are available for fertilization of the ova before the egg-laying. Al- 

 though the zygotes thus formed are laid in characteristic egg-masses, 

 they are not easily collected; full-sized ova may have been seen in 

 dissection of the reproductive organs. In spring and early summer 

 juvenile stages of various locusts and grasshoppers may be collected 

 by sweeping with an insect net the grass of fields where the adult 

 insects abound (Fig. 70). Study as directed by instructor any of the 

 foregoing stages that may be available. 



OTHER INSECTS 



Exercise 1. — The Beetles. 



(a) Any large beetle will do for this study, provided that it is not 

 too highly specialized. Examining the animal from the ventral 

 surface, locate the head, thorax, and abdomen, and note the number 

 of somites visible in each. Look for antennae, compound eyes, ocelli. 



