MisceUa n cous. 4 '> 't 



when i[ono9tomidac were spoken of, it was remarked that tho 

 genus Monostomum had disappeared ; it had slijiped through our 

 fingers ; the only species remaining waa Monostonnim priKrytaticuin, 

 Zeder, which, however, according to Monticelli is a Distomum ; 

 according to Looss tho species is absolutely indeterminable. Thus 

 Zeder's genus Monostomum has ceased to exist, and a similar fate is 

 in store for many another old genus if tho course adopted is 

 followed further. 



While entirely sharing the above-quoted views of Looss with 

 reference to the value of the old names, I cannot approve of the 

 action of this author and others in founding wherever possible a 

 new genus for each new species, nor can I assent to his definition 

 of the idea conveyed by the latter term. Looss declares that, if two 

 different species exhibit anatomical differences, they at least belong 

 to different genera ; two species of the same genus must be in 

 perfect agreement as regards their anatomical structure, and may 

 only difier in the relative size and position of their organs and in 

 actual bodily size. If we examine the figures of the six iJistomes 

 given by Looss on p. 800 of his work already referred to, which are 

 stated to represent six genera, the conviction takes hold of us that 

 specific differences are here mistaken for generic : in fig, 5 the 

 vitellarium lies beneath and outside the limb of the intestine, in 

 fig. 6 only outside it ; otherwise the two figures agree in even the 

 smallest detail ; and these are said to belong to two genera. If 

 trivialities of this sort are regarded as generic differences, we shall 

 soon have as many genera as species. Looss asserts that the old 

 generic designation Distomum no longer signifies anything whatever. 



I consider Distomum to be an excellently characterized genus, 

 which, like Tcenia, only possesses the inconvenience of being too 

 bulky ; we shall therefore do well to effect a division into subgenera, 

 and to write, for example, Distomxim (Ajwhhma) appendiculatum 

 and Tmnia (Davainea) frontina. The definition of a genus adopted 

 by Looss is, however, inapplicable to other classes, e. rj. birds, fishes, 

 and insects. I regard the genus as the aggregate of species united 

 into closer association by means of common characters : thus we 

 have genera such as Felis, Anas, Cijpnnus, Enna, Vi2)era, Vanessa, 

 and in botany Quercu-^ and Ranunculus ; they are not based upon 

 anatomical differences, however; Looss's definition ignores common 

 characters and only takes into consideration the ditferences ; for the 

 concept of a genus, as I apprehend it, it is not the differences but 

 the common features that are decisive. 



In ornithology we have got beyond this period of nomenclature ; 

 time was when the gulls found on German shores bore tho generic 

 designations liodostethia, Xema, Jfi/drocoliPUg, G'avia, Melaqavia, 

 Ccphus, Laroides, liissa, Chimonea, Parfophila, Cetosparactes, Leucus, 

 Glaucus, Clupeilarus, and Dominicanus — fifteen generic names for 

 twelve species ; they are now in the majority of cases all called 

 Larus once more, the three-toed gull at the most is assigned to 

 Rissa. 



