Brajic/iiopoda. 



27 



pools and ditches in many parts of Europe, but it is very uncertain Table-case 

 in its occurrence, and it may suddenly reappear in numbers after ■^*^- ^• 

 an absence of many years. Males are rarely found. It was 

 formerly found in several localities in the South of England, but 

 no British specimens were seen for upwards of forty years, and 

 the species was supposed to be extinct in this country. In 1907, 

 however, it w^as discovered by Mr. F. Balfour Browne, in Kirk- 

 cudbrightshire, and some specimens obtained by him are exhibited. 

 The eggs of Apiis, and indeed of most Branchiopoda, can survive 

 being dried, and they may be carried from place to place in mud 

 adhering to the feet of wading birds 

 or in other ways. There can 

 be little doubt that the recent 

 appearance of the species in Scot- 

 land was due to introduction of 

 the eggs in some such way from 

 the Continent. 



The species of the Sub-order 

 CoNCHOSTRACA havB the body 

 enclosed in a bivalved shell, which 

 resembles very closely the shells 

 of some Molluscs. The genus 

 Estheria (Fig. 8), of which speci- 

 mens are exhibited, is of interest 



on account of its geological antiquity ; fossils referred to the 

 genus occur in rocks of the Devonian period. 



Fig. 8. 



Estheria mcUtensis (slightly en- 

 larged). [Table-case No. 1.] 



Order 2. Cladocera. 



The number of somites is small. There are from four to six 

 pairs of trunk-limbs. The carapace generally forms a bivalve 

 shell, enclosing the body and limbs but leaving the head free. 

 The antennae are large and two-branched, and are used in 

 swimming. 



The Cladocera are generally very small animals, and from their 

 jerky mode of swimming have received the name of " Water-fieas." 

 They are abundant everywhere in ponds and ditches, and a few 

 species are found in the sea. 



One of the commonest species in fresh water is DapJinia pulex, 

 of which specimens are exhibited together wdth an enlarged draw- 

 ing of the animal as seen under a low power of the microscope 



