PLANKTONIO STUDIES. 593 



Radiolaria. — No chiss of organisms has remained so lon^? unknown 

 to us, and by tlie brilliant discoveries of the last decade has been sud- 

 denly placed in so clear a light, as the Eadiolaria (comp, 4, § 251-200). 

 For half a century we knew next to nothing- of these wonderful rhizo- 

 pods; to-day they appear as one of the most important planktonic 

 classes.* These, the most varied in form of all tlie unicellular organ- 

 isms, form a pureli/ oceanic c/a.s'6', and live and swim in all seas, especially 

 in the warmer ones. ]S"umerous species are also found near the coasts, 

 yet tliese are not distinguishable from those of the open sea. They 

 ccmstitute no separate neritic fauna. 



Vast crowds of Radiolaria occur at the surface of the ocean, as well 

 as at different depths. Long* ago Johannes Miiller remarked: 



It is H great plieuomeuon that Acanthomelia cau be takeu daily by tbousauds in a 

 calm sea and iiideiiendeutljr of storms; and that of many spccii s of Pohjcystina, 

 hundreds of individuals were seen during my hist residence at the seashore (2, p. 25). 



I have tried myself, on the hundreds of voyages to different coasts 

 which I have made since 1850, to thoroughly study the natural history 

 of the Radiolaria. The incomparable collections of the Challenger 

 aftbrded me by far the richest material for observation. The results 

 obtained therefrom are embodied in the report (1887). Among- other 

 references to the conditions of the plankton there mentioned, it brought 

 up the following propositions: (1) Radiolaria occur abundantly in all 

 seas which contain a medium amount of salt, and which do not (like 

 the Baltic) receive a strong influx of fresh water. (2) In the colder 

 seas only a few species occur (chiefly Acantharia), but immense quan- 

 tities of individuals; towards the equatcu' the variety in form gradu- 

 ally increases (horizontal distribution, comp. 4, § 220-231). (3) The 

 chief groups of Radiolaria are distributed unequally in the five bathy- 

 zones or girdles of depth of the open ocean. The subclass Porulosa 

 (the two legions of iSpumellaria and Acantharia) inhabit especially the 

 two upper zones. On the other hand, the subclass Osculosa {Nasselaria 



* After Ehronberg, in 1847, had described the siliceous shells of some hundred 

 species from the Barbados, we obtained in 1858 tlie first description of their organ- 

 ization through Johannes Miiller. In the work with which this great master closed 

 his renowned life he described 50 8i)ecie8 which he had observed alive in the Med- 

 iterranean Sea (2). When in continuation of this I devoted a winter's residence 

 in Messina to their further investigation, I was able in 1862, in the monograph con- 

 sequent thereupon, to distinguish 144 new species, iu all 113 genera and 15 families (3). 

 But this rich Ihulioluria fauna of Messina still gave no promise of the immense (fuau- 

 tities of these delicately oruameuted creatures peoi)ling the o])en ocean, and 

 whose variously formed siliceous shells, sinking to the bottom after death, formed 

 that wonderful sediment, the "liadioUtria ooze." This was first discovered thii'teeu 

 years later by the Challenger. The investigation of the fabulous radiolariau treas- 

 ures (chiefly from the i'acihc) which this expedition brought home has led to the 

 discrimination of 20 orders, 85 families, 730 genera, and 4,318 species (4, ^ 256). 

 Further study of the RaiUolarin slime of the deep sea will bring to light many new 

 forms from this inexhaustibly rich mine. 

 H. Mis. 113 38 



