MILLIPEDES 31 



of species of lulus and Spirobolus. Planidium larvae of parasitic 

 Hymenoptera have been found on Gymnostreptus parasitarius in 

 Brazil and a larval Lampyrid beetle introduces itself through the 

 anus into the posterior intestine of Pachyiulus spp. (Remy, 1950b). 

 It is probable that parasites play a negligible part in controlling 

 the density of millipede populations. f Only three classes para- 

 sitise them to an appreciable degree: Acari, which are little more 

 than commensals, Sporozoa and Nematoda which probably cause 

 little inconvenience to their host. 



Reproduction and life cycle 



There is a Malay belief that if the vertebra of a fish is kept under 

 a mattress for some time it becomes a centipede, and that the 

 strands which are found between the pulp and the rind of a plan- 

 tain become millipedes if they are securely bottled up and kept in 

 a dark corner! 



The paired genital openings of millipedes are situated on the 

 third segment just behind, or on, the second pair of legs. In the 

 female, the orifice is surrounded by two sclerotised pieces, one 

 forming the bursa, arranged like the two shells of a mussel with 

 the hinge directed posteriorly and the second, the operculum, 

 covering the gape of the two valves of the bursa. The whole en- 

 semble is termed the vulva and is of diagnostic value. In the male 

 the genital openings may or may not be developed into paired or 

 single penes. The accessory genitalia consist of one or both appen- 

 dages of the seventh segment which are modified to form intro- 

 mittent organs called gonopods, except in the Oniscomorpha and 

 Limacomorpha where the hindermost legs serve this function. 

 These organs are the only criteria for accurate diagnosis: in some 

 species they are retracted within the cavity of the seventh segment. 

 Before copulation takes place the male, by flexing his anterior seg- 

 ments, 'charges' his gonopods from the opening on the third body 

 segment. From the gonopods the spermatic fluid is transferred to 

 the vulvae of the female: fertilisation is internal. 



During copulation the positions assumed by the male and female 

 are somewhat similar in all species. The following description ap- 



t See discussion of density-dependent and density-independent factors 

 on p. 141. 



