XII] COCKROACH 243 



it two cords pass oackward and bear three pairs of ganglia in the 

 thorax and six in the abdomen. This difference between the number 

 of nerve ganglia and the number of segments is carried to a much 

 greater extent in some Insects where, as in Spiders, all the post- 

 oesophageal ganglia tend to fuse into a common nervous mass in the 

 thorax (Fig. 107). 



The only specialised sense organs are the eyes and the antennae. 

 The eyes have fundamentally the same structure as those of the 

 Crustacea : the antennae are the seat of the senses of smell and taste, 

 and are in addition very delicate tactile organs. The maxillary 

 palps are also tactile and are constantly touching and testing the 

 ground on which the cockroach is moving. 



Cockroaches are bisexual. The ovaries in the female consist of 

 two sets of eight tubes ; each tube has developed 



Reproduction. . 1 



trom a coelomic sac in the embryo. They unite at 

 their anterior ends into two cords which pass to the dorsal wall of the 

 thorax and become attached to the pericardial septum, and at their 

 posterior end they fuse into two short oviducts which join to form 

 a small uterus (Fig. 99). Each of the sixteen tubes contains cells, 

 some of which become ova, and as they approach the oviduct the ova 

 become arranged in a single row. At the same time they increase 

 greatly in size by the deposition of yolk in the egg, so that an ovum 

 just before it leaves the body is of considerable size. 



The eggs are apparently fertilised after leaving the uterus by 

 spermatozoa which emerge from the spermatheca (in which they 

 have been deposited by the male) situated behind the opening of 

 the uterus. Whilst still in the genital pouch the fertilised eggs are 

 surrounded by the secretion of the colleterial glands which open 

 behind the spermatheca, and this secretion hardens into the egg- 

 capsule or cocoon. 



The paired testes of the male are functional only during youth 

 and as they diminish in size after they cease to function, they are 

 only to be found with difficulty. They lie concealed by the fat-body 

 below the terga in the region of the fourth, fifth and sixth abdominal 

 segments. They look somewhat like elongated bunches of cherries, 

 their translucent colour strongly contrasting with the opaque white 

 of the fat-body. Two vasa deferentia lead from the testes to a 

 pair of large reservoirs called vesiculae seminales, which together 

 form the "mushroom-shaped gland." Into these at an early age the 

 cells destined to form spermatozoa pass from the testes and there 

 they undergo their further development. The mushroom-shaped 



162 



