171 



The Winter Egg of a rare Water-Flea [Leydigia acantho- 

 cercoides Fischer). 



By D. J. Scourfteld. 



{Bead January 2(V//, 1890.) 



Plate 11. 



There seems no room for doubt at the present day that the 

 production of winter or resting eggs is of universal occurrence 

 among the little animals belonging to the Crustacean sub-order 

 Cladocera, notwithstanding the fact that in many species such 

 eggs have not yet been observed. In the most representative 

 family, the Daphnidse, these special eggs are always enclosed in 

 a very remarkable and complex modification of the shell of the 

 mother, commonly known as the " ephippium," because of its 

 resemblance to a saddle both as regards shape and position. In 

 the other Cladoceran families the production of an ephippium, 

 similar in all respects to that found among the Daplmidse, is 

 extremely rare, the only certain instance, so far as I know, being 

 Macrothrix sjnnosa King, recorded by Professor G. 0. Sars in 

 " Additional Notes on Australian Cladocera raised from dried 

 mud " (7). Nevertheless structures clearly homologous to true 

 ephippia, though usually very much simpler, are found in the 

 families Bosminidse, Lyncodaphnidfe, and Lynceida3. The species 

 belonging to the remaining families of the Cladocera appear to 

 allow their resting eggs to escape freely into the water without 

 providing them with any auxiliary coverings. 



The earliest mention of resting eggs among the Lynceidse, to 

 which family the species dealt with in this paper belongs, is to be 

 found in Jurine's " Histoire des Monocles " (2), published in 1820. 

 In speaking of the smaller forms of the Cladocera which exhibit 

 a very evident eye -spot {i.e. mainly the Lynceidae), he says 

 (p. 148), " La seUe qui couvre leur dos ne contient jamais qu'une 

 seule boule, laquelle est placee au milieu de cette pellicule noire at 

 y fait saillie." He also distinctly refers to the saddle or ephippium 



