310 DR. H. J. HANSEN ON THE [NoV. 29, 



Before concluding this account an apparent exception may be 

 mentioned. In Sars's work pi. 50 is filled with drawings of 

 JVaniioniscus ohlongus G. O. S, The author figures two animals 

 which he believes are female and male of the same species. On 

 the figure representing the male abdomen from below is seen a 

 large undivided opercukun. In the text he says (p. 120) : "It is 

 a very remarkable fact, that the operculum in neither of the two 

 specimens examined showed any trace of the usual transforma- 

 tion, though the male character of the specimens otherwise could 

 easily be demonstrated, both by the greatly projecting sexual 

 prominence, and by the presence of well-developed testes shining 

 distinctly through the integuments in their usual place. In the 

 Caspian species, on the other hand (of which as yet only a solitary 

 male specimen is known), the sexual characters were quite 

 normally displayed." But such differences between the raales of 

 species belonging to the same genus do not exist ; the second 

 pair of pleopoda with its complex organisation for copulation is 

 not wanting in the male of one species, and highly developed in 

 the male of another species of the same genus. What Sars 

 considers to be the male of JSf. ohlongus is in reality a female of 

 another species : I cannot account for the nature of the structure 

 interpreted by him as testes, but the large spine in front of the 

 operculum has nothing to do with the " sexual prominences " 

 of the seventh thoracic segment in a male. I may add that I am 

 very well acquainted with the genus Nannoniscus ; chiefly from 

 the ' Ingolf ' our Museum possesses examples of about ten species, 

 all with the globular or ovate organ at the end of the antennulse 

 also found in the two species described by Sars as N. ohlongus 

 G. 0. S. 



V. Morphological Interpretation of the Pleopoda hi Asellota. 



In the three preceding sections the pleopoda and their parts 

 are mentioned as if the names applied had been generally used 

 or accepted by carcinologists, biit it is far from being so. Some 

 of the interpretations are new, others not generally accepted ; 

 for these reasons it may be useful to give a comparative review 

 of this subject. 



I must admit that I have not looked through many of the 

 descriptions of pleopoda scattered in the literature of the last 

 fifty years or more in order to be able to point out that an author, 

 in the description of a genus or a species, might have proposed 

 one or another of my interpretations ; but I am sure that the 

 major part of them are either new or set forth in some of my 

 earlier papers. In the account of the Crustacea in ' Dijmphna- 

 Togtets zoologisk-botanisk Udb}i;te,' Kjiibenhavn, 1887*, I gave 

 a detailed description (Avith figures) of Eurycope gigantea G. O. S. ; 

 on p. 202 I stated that the three parts of the male operculum are 

 respectively the fused first pair and the endopods of the second 



* I had received and distributed separate copies of my paper in this work by the 

 middle of July 1886. 



