286 . Transactions. 



of rain had fallen, following a drought of five months. The animals make 

 the most of their brief existence by producing numbers of parthenogenetic 

 eggs, so that the pools swarm with animal life for a short time, and then, 

 to preserve the species, the " winter " or " resting " eggs are produced, 

 which can resist desiccation for many months. 



As the pools dry up in the hotter weather the density of the water 

 increases considerably, but these animals seem adapted to withstand such 

 increase. This was noticed of the living specimens kept in the laboratory. 

 The water was not renewed at all, and there was a decided scum formed 

 on the surface of the water, possibly of calcium carbonate from the water. 

 The animals did not seem to suffer in any way from this. 



Spencer and Hall (1896, p. 229) have recorded of Apus a tendency on the 

 part of the animals, as the water receded in the pool, to swim out towards 

 the shallower edges and bury themselves in the mud, instead of keeping 

 in the deeper parts of the pool. Probably, as is suggested, the eggs are 

 protected in this way, although the animals themselves die. 



•When once the pool is quite dry the mud may remain caked and hard, 

 and the eggs therefore stay embedded in it till next rainy season and then 

 develop. Sometimes it may happen that the mud is broken up into dust 

 through various agencies, and the dust so formed scattered by the wind. 

 Then the eggs are carried from this spot to one far distant, and next year 

 there may be no sign of the animal in this particular pool, though in another 

 locality where it was formerly unknown it may be found in abundance. 

 This accounts for its intermittent appearance. Wind is not the only means 

 of dispersal of the eggs. Wading-birds and water-birds may remove them 

 in the mud which cakes on their legs, and so carry them to another of their 

 haunts. 



It seems necessary, however, that the eggs should be subjected to longer 

 or shorter periods of desiccation for their proper development. " The 

 eggs should be dried first and afterwards placed in water. Many eggs float 

 when placed in water after desiccation, the development taking place at 

 the surface of the water" (Weldon, 1909, p. 32). 



All the attempts to hatch out the eggs in October, 1916, in the labora- 

 tory have been unsuccessful. 



In New Zealand Lepidurus viridis usually makes its appearance about 

 September or October, though those collected at Cashmere bear the date 

 December, 1904. There is, however, no further record of them. Mr. G. E. 

 Archey tells me that in 1912 he saw in shallow pools near New Brighton 

 many specimens of Lepidurus swimming about under a thin coating of ice, 

 but he has kept no record of the month. 



The first collection brought alive into the laboratory consisted of about 

 eighteen animals from Linwood on the 23rd September, 1916. Six of these 

 were placed in a large aquarium-jar containing water about 3 in. deep, 

 together with a small quantity of river-weed, Elodea canadensis. The jar- 

 was left in a window facing south. Most of the specimens were females 

 bearing a large number of deep-orange-coloured eggs in the ovisacs. Some 

 of these eggs were discharged into the water, and it was noticed that the 

 animals that discharged them died very shortly afterwards. These con- 

 ditions were evidently not suitable, for all the animals were dead within 

 five days. 



The greater number of this first collection was left in a large enamel 

 bowl on a bench in the centre of the large laboratory away from direct 



