BIHANG TILL K. SV. VET.-AKAD. HANDL. BAND. 20. AFD. IV. N:0 2. 9 



called a species or not. * I do not think the question can be 

 .scientifically solved in any otlier way. Bnt this work can 

 liardlj^ be done b}^ one man alone. nnless he lias the oppor- 

 tunity of devoting all his time to this subject, and that is 

 the reason for me to publish the resnlts of these researches 

 now. even in their incomplete state. 



F'inally, I can not forbear to treat the old question 

 whether O. F. Muller'^ Daphnia longispina is maintainable 

 as species. Few species have been proposed which have cansed 

 afterwards so much confasion in the nomenclatni*e as this one, 

 and the reason is. as it seems to me, very easily understood 

 from what 1 have written above. For one may he pretty 

 sure that, if there are several genuine species in this group 

 (not Hyalodaphnia). there must also be several longispina- 

 forms, and so one can easily understand. wliy it was so 

 difHcult to find any agreeinents between them. Above all O. 

 F. Muller's ^) iigures of his Dnphnia longispina (Pl. XII, f. 

 <s — 10) have caused confusion and been interpreted now in one 

 now in another way. For my own j)art I think the posterity 

 lias done wrong to Muller in giving so nuich importance to 

 these figu]'es. Muller seems not to liave been able himself to 

 draw; tlie figures were drawn by his brother and. moreover, 

 tliey were not published till after his death. If we leave ont 

 of sight the Iigures, the question is fairly simple. De Geer ^) 



distinguished two species >Monocidus {Pulex ramosus) 



/( .s-^^ posfire anispinosa, and yfMonoculus (exspinosus) ■ 



frsta posfire rofumlafa tion spinosa. The first one is MiiLLERS 

 longispina according to his own list of synonyms, the secoRd 

 is, according to general opinion, Muller's Daphnia sima. 

 ]\[uller's figures are so badl}^ drawn, that it is härd to tell 

 what they represent. If I dared to add to the number of 

 suppositions, I should guess that it was a form of Hyalo- 

 daphnia. But in ni}' opinion Muller comprehended in his .species 

 all the longis2) ina-f ormfi he did know. This is strengthened 

 by his diagnosis as well as by his quotation of De Geer. 

 ( )n the othei' hand he comprehended older specimens without 

 s])ine. but with mucro (corresponding particularly well with 

 my fig. 9 etc.) in his species pennata. From the fact, that 

 he found it as late as in the month of November (1. c. p. 86) 



* For such researches the freshwater l)iological stations must be very 

 suitable places. 



