Protistplankton. 



123 



Mori'ovtT. I liavc bcni cniililtMl, l)y kiiiil assistance from differ- 

 riii (|iiart('rs. to obtain soiiic ricluT nulioiaria samples — most of 

 tlifiii. luifortuuateiy, of fossile species — , which, althoufrh 1 have not 

 yet hy far been able to work them tiirougii, as far as I can see, show 

 that my opinion of the strnctnre of this division of NasseUaria is 

 on the wliole correct. 1 iiope in the futnre in a more detailed 

 work to be able to eive more exact leasons for my opinion, and 

 try to apply it consistently to the more important i:enera of ^V^s- 

 scllariii. 



My remark, that Hakckel had to some extent ijruored certain 

 piimary skeleton parts, which I consider to be the principal type 

 fur all the forms which I have examined, may give rise to some 

 niisnnderstandiny. Haeckel several times draws special attention 

 to the ..basa'l tripodium" as a ground plan, from which a large 

 number, perliajis all. of the forms may be developed. This triradial 

 iiTonndplan also lies at the bottom of certain classitications in his 

 system. According' to my opinion, thei'e is something wanting 

 here — of which more further on — which is of gi-eat import- 

 ance. Thus I found, quite at the beginning of my work with 

 XasseJlaria (.IihuiExsEx L. 91 1 that Claparede's genus Playiacantha 

 was of lUfferent structure than Haeckel (and Clapahede) had de- 

 scribed, and, unfortunately, proved to have the same structure which 

 Haeckel describes as characteristic for other genera (Plagonidium 

 HcK., Plagiocarjya Hck., Peripleeta Hck.). 



This peculiar structure is, however, not contined to radiolaria 

 beloHL^'ing to the genera mentioned, but is common to the whole 

 division, \\-itli variations in development in ditferent directions (see 

 below). 



This circumstance of itself makes it impossible to retain Haeckel's 

 g"enera in their original detinition. 



Whoever has tried to use Haeckel's system of classification 

 of Xassellariu foi' other divisions, as, for instance, the large one 

 C'l/rtoiden, must certainly have found that the genera and divisions 

 of his system are, at any rate in part, unsatisfactory and prove not 

 to be so well limited as to be of practical service. In several 

 instances, certain secondary structural conditions of comparative 

 insignificance are taken to be a basis for division, as also, in not 

 a few cases, accidental and passing stages of development are 

 used as distinctive characteristics. Especially in several of the 

 ( 'l/rtoi(Jca in my material there are — and must be according to 

 my oiiinion — real radial apophyses, which are not found in the 

 corresponding genera according to Haeckel, so that they would 

 have to be classified under quite different divisions in his system. 



On this account, I have been obliged to start new genera 

 here too. 



It seems to me that taken as a whole, Haeckel's system as 

 regards the XanseUaria, — at any rate, large portions thereof — 

 must be entirely reconstructed. It will then be possible to retain 

 a large number of Heackels genera, but with different definitions. 



Haeckel mentions several times that the Xassellaria can 

 monophyletically be traced from an oi-iginal ground form, but that 

 great difficulties are met with when one tries to put this into practice. 

 He states that „the basal tripodium" or a sagittal ring or a ce- 

 phalis may be looked upon as such a ground form. He seems, 

 however, to consider the tiipodium as the most natural starting 

 point, as there are traces of such a tripodium to be met with in 

 the ring species and Ci/rtoidca (..cortinar feet" in Cortimi and Cor- 

 tiniscus, „cortinar septum" in several Ci/rfoidea). 



This tripodium corresponds best also to my ideas. 



As a foundation for the detailed desciiptidn which follovFs, I 

 have, had to coin various designations which arc most easily ex- 

 plained together when giving a comparative treaty of the whole 

 group. Then too, I will explain my ideas with regard to the re- 

 lation one to another, and the origin, of the g-enera found in the 

 material under examination. 



Pliylogeny of the genera mentioned. 



As an original gi'ound foi'm, 1 take oni; which is similai' to 

 Plagonidium Hck. (and Plagiocarpa Hck.) and which has four 

 spines, extending in twos divergently from the ends of a short 

 central rod. 'Vho plane thi'ough two of them, the sagittal plane, 

 is perpendicular to the plane through the other two. 



With a change of direction, an apical spine, A, and .3 basal 

 ones will soon appear. These basal spines are one of them dorsal^ 

 D (fig. I) and two lateral, Lj. (right) and Lj (left). 



This seems to be a natural 

 form for the skeleton, con- 

 sidering the position of the 

 central capsule. (Cfr. below, 

 concerning the position of ba- 

 lance in the water). 



These 4 primary spines 

 are, as stated in my previous 

 paper (L. 91), the same as 

 constantly occur in the Xassel- 

 laria which I mentioned. There 

 they were called : Der primare 

 Mittelstachel (= D), der Vor- 

 derstachel (^ Li) and der 

 Hinterstachel (= Lj.). :My 



reason now foi' changing the 

 names is that the designations 

 used will continuallv recur in 



., . , , . ,.' , . , Fig-. I. The ground form: lateral view, per- 



the special descriptions, which ^ ,. , „ , ,. „ „ ,, » „ . 



' ^ ' spectively. Schematically, as the foUowiiis.' 



it would not be at all easy to " figures, 



understand unless I gave these 



spines their special names, so that it was important to choose 

 suitable ones, and such as agree as far as possible with the designa- 

 tions used by Haeckel, whereever these latter could be retained. 

 If the skeleton be placed so that the central rod is horizontal 

 and seen from the ventral end, the sagittal plane being vertical 

 and the apical spine directed upwards, then the primary dorsal,, 

 basal spine D will be directed backwai-ds and downwards, the 

 apical spine A somewhat backwards and upwards, the left, lateral 

 spine Lj (from the ventral end of the central rod) downwards, 

 forwards and to the left, and the right, lateral spine L^. downwards,. 



forwards and to the right (fig. II and fig. HI). 



Now there arises. a verticil of 3 branches on each main spine, 

 and so we have the Plagiacantha type, as it is found in the spe- 

 cies P. arachuoides Clap, (not the genus Plngiaeantha Hck.). 



The apical spine is here rather small and has (generally?) only 

 two branches. 



ily reason for considering the apical spine, nevertheless, as be- 

 longing to the primary skeleton, is that I have never come across- 



