on some British Millipedes. 287 



retaining this hold until the body of the female is for most 

 of its length embraced in the broader grasp of the male. In 

 marked contrast with Glomeris, copulation lasts a long time, 

 usually two days or more, and takes place only once. One 

 naturally couples this with the fact that the Polydesmus 

 female also lays all her eggs at one time. 



It is interesting to note that a fertilized female, when 

 touched on the anal segment by a male, immediately darts 

 forward and refuses to be caught. With a camel-hair brush 

 the fertilized females in a collection can be readily recognized 

 by touching lightly on the anal segment. 



About three weeks intervene between fertilization and nest- 

 building. Again, in striking contrast with Glomeris, the 

 eggs of the Polydesmids are all enclosed in a common 

 covering. This nest is a thin-walled, particularly well-made 

 dome-shaped tent, surmounted by a narrow tubular chimney. 

 The nest ia built on a firm substratum — a stone, a leaf, the 

 inside of an acorn-cup, or the inner surface of apiece of bark. 

 In one respect, however, Polydesmus agrees with Glomeris 

 and other Diplopods, viz. that the whole of the building- 

 material passes through the gut, or, in other words, is com- 

 posed of excrement made fluid with a secretion that hardens 

 on exposure, and that the whole of the building is done by 

 the very mobile surfaces of the extroverted rectum. A great 

 deal of discretion is employed in the selection of a suitable 

 building-site. If a stone is selected, the building is done on 

 a spot with a slightly concave contour ; if a smooth patch of 

 firm soil or bark, then the female eats out a concavity in it. 



The site being selected, the female bends itself into a circle 

 and walks round and round, leaving a rapidly drying blob of 

 excrement behind it as it goes, until the concave spot is 

 surrounded by a rampart the circumference of which is 

 slightly greater than the length of the animal. This rampart 

 is built in such a way that a section across the edge would be 

 roughly triangular in outline, being broad at the base and 

 thinning off as it rises. The construction of the sides and 

 roof demands far greater skill and precision, on account of 

 the extreme tenuity and the graded roundness of the dome. 

 For this purpose the everted rectum is no longer used as a 

 trowel for plastering, but the blob of material is moulded, as 

 if between finger and thumb, into a thin layer, and held in 

 position, until it is sufficiently well fixed, by the two apposed 

 sides of the rectal wall. Meanwhile the animal walks round 

 the rim as before, adding new pieces as it goes, each piece 

 slightly overlapping the one behind and below it, like tiles on 

 a roof. When the nest has reached about two-thirds , its full 



