MILLIPEDES 35 



among different orders and also among different species of the 

 same order. There is a tendency for the size of the egg to decrease 

 in direct proportion as the number of young per brood increases. 

 It follows from this that the differences in the total amount of yolk 

 contained in various broods, whether they contain a large number 

 of small eggs or a smaller number of large eggs tends to be evened 

 out. Polyxenus lagurus only lays from 10 to 20 eggs with 4 to 8 per 

 nest, but species of Polydesmus lay between 100 and 200, Oxidus 

 gracilis up to 300, lulus spp. lay 60 to 100 or more, and some of the 

 Spirobolidae may also lay up to 300 eggs. The maximum recorded 

 clutch of Arctobolus marginatus in Washington was 261. 



Incubation of the eggs may take several weeks before hatching 

 occurs. This process is assisted by a strong conical egg-tooth situa- 

 ted, in the Opisthospermophora, on the middle of the head. 



Glomeris marginata seeks no special protection during moulting, 

 but does so in some loose earth or on the surface under moss or 

 dead leaves. The case of both Proterospermophora and Opistho- 

 spermophora is very different. The millipedes of these orders 

 build moulting chambers which are essentially similar to their 

 nests. If the moulting chamber is damaged so that other millipedes 

 can enter, the helpless animal that has just shed its skin is almost 

 invariably eaten up by the invaders. After moulting it is customary 

 for millipedes to eat their cast exuvium, thereby restoring lost 

 supplies of calcium: further development does not proceed nor- 

 mally unless they do so. 



All Diplopoda are anamorphic and the larvae pass through a 

 number of moults during each of which the number of legs and 

 post-cephalic somites is increased. Additional legs and somites are 

 added in the embryonic region between the anal somite and the 

 one that was last formed. Colobognatha, Ascospermophora and 

 Proterospermophora pass through seven larval stadia, in each of 

 which the number of leg pairs and somites is constant for the 

 species or the group. The Opisthospermophora also normally pass 

 through seven larval stadia but after the first or second the number 

 of legs and somites is not constant for the species. In the Onis- 

 comorpha, development is hemianamorphic: a series of ana- 

 morphic moults is followed by three moults which are unaccom- 

 panied by increases in the number of legs and somites (Verhoeff, 



