INTRODUCTORY REMARKS. 



The collection dealt with in the present paper is extremely large, both 

 as to the number of species, sixty-three, and especially as to the numbers of 

 the specimens of the major part of the forms. A small portion of the material 

 was captured by the late Alexander Agassiz near the Fiji Islands in 1897, a still 

 smaller lot was secured during the trip of the "Albatross" in 1899-1900, but 

 the vast majority has been collected by Dr. Agassiz in 1904-1905 in the Eastern 

 Pacific. When we wish to get a closer insight into the whole topic it is, how- 

 ever, necessary to consider separately the two orders still not infrequently 

 united under the name Schizopoda, viz. Mj'^sidacea and Euphausiacea. And a 

 comparison with the results of the exploration of the Dutch "Siboga" Expedi- 

 tion in the Indian Archipelago is interesting. 



Of the order Mysidacea only twenty-three species are at hand, fifteen of 

 which were secured in 1904-1905, while the remaining eight forms were exclu- 

 sively gathered during the earlier trips just mentioned. Fifteen species in all 

 from the Expedition in 1904-1905 is in reality a small number as compared with 

 the number of species already known of this order. But the explanation of this 

 fact is given below, and when we consider the order Euphausiacea the aspect 

 is quite different. Of the last-named order the collection contains forty species, 

 all with a single exception taken in 1904-1905 (some among them besides in 

 1899-1900 or off the Fiji Islands), but as only seventy-three species of this order 

 are known from all seas, it will be seen that Dr. Agassiz during that single 

 Expedition captured more than half of the world's fauna. The "Siboga" 

 gathered only twenty-five species of Euphausiacea but no less than forty-seven 

 species of Mysidacea. The explanation of this startling difference between the 

 results of the Agassiz Expedition of 1904-1905 and the "Siboga" Cruise is that 

 the Euphausiacea are nearly all true oceanic forms, while the majority of the 

 My.sidacea either inhabit shallow water, or live pelagically, or not far from the 

 bottom to a few hundred fathoms and within no very great distance from land. 

 And while the "Siboga" in the main explored the straits and comparatively 



