THE 
VOYAGE OF H.M.S. CHALLENGER. 
ZOOLOGY. 
REPORT on the N tjdibr anchiata di’edged by H.M.S. Challenger during 
the years 1873-1876. By Dr. Rudolph Bergh, Physician to the 
General Hospital of Copenhagen. 
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Judging from the number and variety of the species of Nudibranchiata that have 
been hitherto described from the shores of the tropical seas, it is probable that this part 
of the world will ultimately prove to be the headquarters of the group. Although up to 
the present the tropical Nudibranchiata have been but slightly examined in comparison 
with the northern species, nearly every exploring expedition that has visited the 
tropics has discovered new and interesting forms of these animals. The Families of the 
Nudibranchiata are by no means evenly distributed in the different oceans. Of the 
fEolidiaclse by far the greatest number of species inhabit the northern seas, and only a 
few species have been described by van Hasselt, Kelaart, Alder and Hancock, Collingwood, 
Semper, and others, as occurring in the tropical seas . 1 On the other hand, the large 
and important Family Dorididse is more abundantly represented both generically and 
specifically in the tropics. 
Since the main object of the Challenger Expedition was the investigation of the deep 
sea, the number of dredgings made in shallow water was comparatively few ; accordingly, 
as might have been expected, the number of Nudibranchiata collected during the voyage 
1 Van Hasselt only discovered three species, Elliot four or five, Kelaart nine, and Semper four. 
Collingwood (Observations on the distribution of some species of Nudibranehiate Mollusca in the China seas. 
Ann. and Mag. Nat. Hist., ser. 4, vol. i., 1868, pp. 90-94) calls attention to the scarcity of Nudibranchiata on the 
shores of China, Formosa, Lahuan, and Singapore, with respect both to the number of species and of individuals, and 
contrasts with this the comparative abundance of the group on the English shores. Among the Nudibranchiata 
collected by Collingwood there was not a single representative of the Family iEolidiadse. 
(ZOOL. CHALL. EXP. PART. XXVI. — 1884.) Cc 1 
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