Prof. E. Hackel on the Calcispongige. 421 



Synop. Frams. af Sveriges Oniscider (1858), p. 10; Zaddach, Synop, 



Urust. Prussic. Prod. p. 17 ; Fric, Die I^'ustenthiere Bohmens (1872), 



p. 2o6. 

 Zta afftlis, Koch, Deutschl. Crust, xxxiv. f. 22, 23. 

 Ligidium [hypnortimj Budde-Lund, Naturhistorisk Tidsskrift, 1871, 



p. 22(5. 

 Zia Saundersii, Stebbing, Ann. & Mag. Nat. Hist. 1873, ser, 4, vol. xi. 



p. 286. 



Ligidium agile has a wide European distribution, and has 

 been found in Sweden, Denmark, Prussia, Bohemia, and 

 France. It might therefore have been expected to be found 

 in Great Britain, especially as Latreille's specimens had been 

 received from the shores of the British Channel ("Habitat in 

 littoribus Oceani Britannici, ab entomologo Brebisson mihi 

 transmissus "), 



The relationship of the species to Ligia rather than to 

 Oniscus was first pointed out by Fabricius, who, in his ^ Suppl. 

 Entom. Syst.,' though he assigns it to Oniscus^ asks "An 

 potius LigiaV 



As has been already mentioned, Koch described two other 

 species, which, however, are perhaps mere varieties of L. agile. 

 More recently Schobel has described a form, under the name 

 of Ligidium. amethistinum^ as distinct from L. agile. Perliaps 

 this species also is destined hereafter to reward the careful 

 search of some British carcinologist. Very little has as yet 

 been done among our land Crustacea, my lamented friend 

 Dr. Kinahan being the only British naturalist who has paid 

 any attention to the Isopoda Aerospirantia. 



XLIX. — On the CalcispongiaB, their Position in the Animal 

 Kingdom, and their Relation to the Theory of Descendence. 

 By Professor Ernst Hackel. 



[Continued from p. 262.] 



II. The Calcispongige and the Theory of Descendence. 



1. Principles of Classification. 



The task which we had set before us as the primary object in 

 this monograpli of the CalcispongiaB, the analytical solution of 

 the problem of the origin of species, has been followed out in dif- 

 ferent ways in the first and second volumes. In the first 

 volume, and especially in its second section, the " Morphology 

 of the Calcispongige," I have endeavoured to describe all tlic 



