CRUSTACEANS 



pigment, called the eye-spot. What may be its precise function is not 

 perhaps precisely known, but if that function be not visual the species 

 of Monospilus must be blind, for they have the eye-spot, but apart from 

 that they have no eye. 



In Mr. Scourfield's various papers many interesting observations are 

 given on the species above enumerated. It would take up too much 

 space to give adequately even a summary of all this valuable information, 

 but attention may be called to one branch of his researches which may 

 be regarded as exceptionally important. In a paper on Leydigia acantho- 

 cercoides (Fischer), a species closely related to L. quadrangular^ (Leydig), 

 he says : ' 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, not- 

 withstanding the fact that in many species such eggs have not yet been 

 observed. In the most representative family, the Daphnidas, 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 Daphnida?, 

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

 Macrothrix spinosa, King, recorded by Professor G. O. Sars in Additional 

 Notes on Australian Cladocera raised from Dried Mud. Nevertheless 

 structures clearly homologous to true ephippia, though usually very 

 much simpler, are found in the families Bosminidae, Lyncodaphnidae and 

 Lynceida?. 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.' ' 



Mr. Scourfield then proceeds to point out that already in 1820 

 Jurine ' distinctly refers to the saddle or ephippium in the case of 

 Cbydorus sphcericus, that Schodler in 1846 records of Eurycercus lamel- 

 fatus, ' that a number of winter eggs were deposited at one time in the 

 almost unmodified cast shell of the mother, a fact which has since been 

 confirmed by Weismann,' that by Kurz in 1874 protective coverings for 

 the winter eggs were reported ' in some sixteen species belonging to the 

 genera Camptocercus, Alona, Plearoxus, Chydorus, etc.,' and that slightly 

 later, in 1 877, ' Weismann independently discovered the resting eggs of 

 several species of the same family ' [Chydoridas], while since that time 

 ' the resting eggs of many other species have been alluded to, in more 

 or less detail, by various writers.' In an earlier paper Mr. Scourfield 

 says : ' Compared with the highly evolved " ephippium " which is formed 

 by the Daphnidz for the protection of their resting eggs, the arrange- 

 ment in Cbydorus spbcericus (and other species of the Lynceidse) is 

 manifestly very primitive, and although both are fundamentally the same 

 I would suggest that the simpler structure be distinguished as a proto- 



1 Journal ef the Quekett Microscopical Club, vol vii. p. 171 (1899). 



215 



