59 



the shape of the megasclera; these are often very abnormal in appearance and may even 

 (though rarely) become oxeote . . . ." Thiele found strongyla in Spirastrcl/a insignis and pcuiis. 

 Although on the whole I believe the oxea to be foreign, in B. M. 31 they resemble modified 

 tylostyli. At all events the tylostyle seems to be the typical megasclere; this is in accordance 

 with the statements of the majority of previous authors. 



II. Mier oscleres. 



Perhaps even more variable than the tylostyli are the spinispirae. We have seen before 

 that they are sometimes very scarce and may even be absent. In specimens where they occur, 

 there are always minute ones ; in others we find larger spinispirae as well, and in many cases 

 they are very robust or very long. I could not make out the question whether in such cases 

 we have to do with two sorts of spinispirae or not. So much is certain that the larger ones 

 have been small in the beginning, and that in several cases we find every possible intermediate 

 size between the smallest and the largest specimens. Under these circumstances it seems to 

 me better to treat them as one sort and to take into account only vvhat is actually observed. 

 As it would be totally wrong to exclude e. g. 1365 and 1971 from Spirastrcl/a because no 

 spinispirae are found, it would be as wrong to make a specific difference between specimens 

 with or without robust spinispirae, again because of the manifold transitions. We have seen 

 that in habitus B.M. 10 and B.M. 13 are intermediate between g2a-l and 300; but in the 

 latter robust spinispirae are absent. B.M. 10 likewise is a link between g2a-l and 1949; the 

 larger spinispirae of the latter are of an intermediate size. On the whole we find the robust 

 form of spinispirae in specimens of trop. tegens and trop. tubcrosa ; they are absent in trop. 

 digitata, trop. g/aebosa, trop. concrescens and trop. tubulifera ; in trop. pyramidalis they are 

 present or absent. In the three specimens of Spirastrclla decumbens I examined, there is a 

 considerable difference in the size of these spicules: in B.M. 38 and B.M. 39 (Pb VIII, figs. 2 

 and 4) they are larger and thicker than in B.M. 27 (Pb VIII, fig. 1). In the two specimens 

 of bistellata we find the same difference: in G.M. 73 (Pb XII, fig. 9) they have about the 

 size and shape of decumbens B. M. 38, whereas in M. N. 44 (Pb XII, fig. 8) they are again 

 still larger. Moreover they are, especially in the latter, more compact (resembling "Doppelsterne). 

 An intermediate condition we find in Spirastrella trausitoria B. M. 30 (Pb XII, fig. 6). In 

 426 a-d we have another interesting series; in 426c! (Pb IX, fig. 6) we find a large quantity 

 of very robust spinispirae-, in 426a (Pb IX, fig. 4) these spicules are considerably smaller; the 

 same is true for 426 b and 426 c (Pb IX, figs. 5 and 7). Moreover they are in the latter not 

 so abundant by far. 



After all what has been said about this question in the course of this paper, I suppose 

 these examples are sufficiënt ; they might easily be augmented. Consequently, if we do not 

 want to consider the various spinispirae we find here, as so many different sorts, we are led 

 to see in them one sort, which is modified into endless variations. The spinispirae may become 

 very large and robust; striking examples hereof we find in: B.M. 38 (Pb VIII, fig. 2 *, /x); 

 B.M. 39 (PI- VIII, fig. 4 p); 426 d (Pb IX, fig. 6 (3, 7 ,S); B.M. 3 (Pb X, fig. 7 y— Q, G.M. 73 



