304 PERIPATUS, MYRIOPODS, AND INSECTS. 



with the tracheae there are large air sacs which aid greatly in 

 flight. 



The circulatory system is in essentials the same as that 

 of the cockroach. The blood contains a few nucleated 

 amoeboid corpuscles. 



The excretory system consists of numerous fine Mal- 

 pighian tubules which open into the small intestine. 



Reproductive System. 



In the drone the reproductive organs consist of a pair of 

 testes, each furnished with a narrow vas deferens, expanding 

 at its distal end into a seminal vesicle. The seminal vesicles 

 open into the ejaculatory duct, and at their junction a large 

 paired mucus gland opens. When maturity is reached the 

 testes diminish in size, while the spermatozoa accumulate in 

 the terminal expanded part of the ejaculatory duct, and there 

 become aggregated into a compact spermatophore. With 

 the terminal portion of the male duct copulatory organs 

 are associated. 



Mating takes place only once in the life of the queen, and 

 is followed by the death of the drone. 



In the queen the large ovaries occupy considerable space in the abdo- 

 minal region. As usual, each consists of numerous (100-150) ovarian 

 tubes containing ova in various stages of development. The ovarian 

 tubes open into the right and left oviducts, which again unite to form the 

 common oviduct. With the anterior portion of the common duct the 

 globular spermatheca is associated. In connection with it there is a 

 gland corresponding to the mucus gland of the male. The oviduct 

 terminates in a copulatory pouch. 



Previous to laying, the eggs are fertilised by sperms set free from the 

 spermatheca. In the case of drone eggs this liberation of spermatozoa 

 does not take place, and the eggs in consequence are parthenogenetic. 

 Queens which have never mated, or which have exhausted their stock of 

 male elements, habitually lay drone eggs, but those which are laying 

 abundant fertilised eggs at times also lay unfertilised eggs. This with- 

 holding of spermatozoa is said to be "voluntary," and related to the 

 needs of the colony, but the physiological reason is unknown. 



The workers possess female organs similar in type to those of the 

 queen, but of an extremely rudimentary nature. 



The eggs are laid singly in the cells of the comb, at the rate of about 

 two per minute, for weeks together. They are of the usual insect type. 

 According to the size of the cell in which it is deposited, and the food 

 with which it is furnished, the fertilised ovum develops into a worker 

 or into a queen. The development takes place within the cell, and 

 includes a complete metamorphosis. 



