PLANKTONIC STUDIES. 575 



The excnrsiou to the coral reefs of the Red Sea (1873), which is 

 recounted in my "Arabic Corals," and the trip to Ceylon, about which 

 I have written in my " Indian Journal" {Indische Reisebrief e, 1SS2), 

 were extremely valuable to me, because I thereby gained an insight 

 into the wonders of the Indian fauna and flora. On the journey from 

 Suez to Bombay (in November, 1881), as well as on the return from 

 Colombo to Aden (in March, 1882), I was able to make interesting 

 observations on the pelagic fauna of the Indian Ocean, as well as dur- 

 ing a six weeks' stay at Belligam and in the pelagic excursions which 

 I made from there. I obtained thereby a living picture of the oceanic 

 and neritic fauna of the Indo-Pacific region, which differs in so many 

 respects from that of the Atlantic-Mediterranean region. The special 

 results of my experience there are, with the kind consent of Dr. John 

 Murray, for the most part embraced in my report on the Radiolaria 

 (1887), and on the Siphonophora (1888), which form i^arts xviii and 

 XXVIII of the Challenger Report. These two monographic reports also 

 contain many observations on plankton, which I had made in earlier 

 journeys and had not yet published. 



The extensive experience which I had gained through my own obser- 

 vations of living plankton during a period of three decades was well 

 filled out by the investigation of the large and well-jireserved planktonic 

 collections placed at my disposal from two different sources by Capt. 

 Heinrich Rabbe, of Bremen, and by the Challenger directors of Edin- 

 burgh. Capt. Rabbe, with very great liberality, turned over to me the 

 valuable collection of pelagic animals which he had obtained on three 

 ditlCTent trips (with the ship Joseph Haydn, of Bremen) in the Atlantic, 

 Indian, and Pacific oceans, and which he had carefully j)reserved 

 according to my directions and by approved methods. This extraor- 

 dinarily rich and valuable material, contained in numerous bottles, 

 embraced planktonic samples from the most diverse localities of the 

 three oceans, chiefly in the southern hemisphere. Like the much more 

 extensive collection of the Challenger, it gives (though to a smaller 

 degree) a complete summary of the complexity of the composition of the 

 plankton and the difference in its constituents. Rabbe's collection 

 supplements that of the Challenger in a most welcome manner, since the 

 course of the Challenger was southward from the Indian Ocean through 

 the Antarctic region, and between the Cape of Good Hope and Mel- 

 bourne was always south of 40° south latitude. The course of the Joseph, 

 Haydn, on the other hand, on the repeated voyages through tlie Indian 

 Ocean, was much more northerly, and between Madagascar, the Cocos 

 Islands, and Sumatra included a number of points where the pelagic 

 net obtained a very rich and peculiarly constituted capture. I hope 

 to be al)le to publish soon in detail the special, results which I have 

 obtained by investigation of Rabbe's plankton collection, with the aid 

 of the carefully kept journal which Capt. Rabbe made of his observa- 

 tions. Tlie discoveries of new radiolaria, medusie, and siphonophores 



