WHiLE working up the enormous material of Crustacea collected by the Danish 

 research-steamer "Thor" during recent years in the Mediterranean and the 

 adjacent parts of the Atlantic^), I observed in the autumn of 1912, that 2 specimens 

 of the Mastigopus-stage of Sergestes vigilax had copulatory organs. This is, as far as 

 I am aware, the only known occurrence of such organs in non-adult Decapoda, though 

 it is evident that large organs with so complex a structure cannot suddenly appear 

 in the adult stage, but that several moultings are necessary to give them their shape. 



When I found these organs, I was not aware that they were known already, 

 and searching in the Zoological Record I could not find information about them. 

 Later on, for quite other reasons, I asked Dr. Angelo Senna in Florence to send 

 me some papers on the Mediterranean Crustacea, and in one of these papers (Le 

 esplorazioni abissah nel Mediterraneo del R. Piroscafo Washington nel 1881, II, Nota 

 sui Grostacei Decapodi ; BoUetino della Sociota entomologica Italiana, Anno XXXIV, 

 Trimestre IV, 1902 (1903), PI. 11, fig. 8) I found a figure of the copulatory organ 

 of the Mastigopus of the species in question. In the same ])aper (p. 292 — 93) Senna 

 has given figures of the organ of the adult, and now recently also Dr. Otto Pesta 

 in Vienna has given another figure (Zool. Anzeiger, vol. 42, No. 9, 29. Aug. 1913, p. 406). 



My own investigations however have not therewith been rendered useless, my 

 material being much larger than what has been at the disposal of the two authors 

 mentioned ; for I am able to give a complete series of the development. 



1. Petasma of the Mastigopus-stage (fig. 1 — 2). 

 Fig. 1 shows the petasma of a Mastigopus, 14 mm, "Thor" St. 206 (39° 32' N, 

 5°15'E), 1000 m wire out; fig. 2: Mastigopus 17 mm, St. 22 (38°50'N, 15°18'E), 

 200 m wire out. 



^) How immense this material is, may be seen from the circumstance, that e. g. of Hyperiidea 

 alone about 3000 samples were brought home before 1913, several of which contain 6-8-10 species. 

 The scientific results are under publication with the title : Report on the Danish Oceanographical 

 Expeditions 1908 — 1910 to the Mediterranean and adjacent seas, published at the cost of the Carls- 

 berg Fund under the superintendence of Johs. Schmidt, Ph. D. — Till now (Sept. 1913) 2 volumes 

 have appeared. 



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