74 



GEODIA JAPONICA. 



It is known that sometimes the amphioxes of tetraxonid sponges are bifur- 

 cate at one end. Such forms are, however, very rare and usually considered 

 pathologic. In the specimen of Geodia japonica examined by me large stout 

 amphioxes, bifurcate at one end, are remarkably frequent. I found no less 

 than six in one spicule-preparation. The two branches of these bifurcate amphi- 

 oxes are equal or unequal and 10-80 /x long. The angle they enclose is always 

 small; the largest observed was 12°. When very short the two branches are 

 nearly parallel to each other and appear as terminal spines. 



The rare large styles are 2.1-2.8 mm. long; their maximum thickness is 

 40-43 n; the rounded end measures 10-31 //, about one third to two thirds of 

 the maximum thickness in transverse diameter. Such spicules are not men- 

 tioned either by Sollas or Thiele. I found them, however, in Sollas's type. 



The large slender amphioxes (Plate 37, fig. 22d) are strongly and very 

 irregularly curved, 1-2.2 mm. long and, in the middle, 12-22 fi thick. Their 

 ends are exceedingly slender, thread-like. Though not mentioned by Sollas 

 or by Thiele, I found such spicules in Sollas's type. 



The minute dermal amphioxes (Plate 39, figs. 1-9) are usually somewhat 

 anisoactine and rather abruptly pointed. They are straight (Plate 39, fig. 9) 

 or more or less, sometimes very considerably curved, usually in an irregular 

 manner (Plate 39, figs. 1-8). They are 195-280 /x long and, in the middle, 

 3.5-7 fj. thick. In Sollas's specimen they were small and fusiform. Thiele 

 gives their length as 300 fi. Neither Sollas nor Thiele mentions the remarkable 

 irregular curvature of so many of them. In the type of Sollas reexamined by me 

 these spicules are 190-270 fi long and 3-6 /x thick. Most of them are more or 

 less anisoactine, and some strongly and irregularly curved. 



The rare minute dermal styles are not so strongly curved as the amphioxes, 

 somewhat shorter, and in the middle 5.5-6.5 /i thick. The rounded end is 2.4- 

 3.5 jw, about half the maximum thickness of the spicule in transverse diameter. 

 These spicules can be considered as derivates of the minute dermal amphioxes 

 in which the anisoactinity has been carried to the extent of the rounding off of 

 the proximal end. I found such spicules in Sollas's type though they are not 

 mentioned by him or by Thiele. 



The orthotriaenes and plagiotriaenes (Plate 37, figs. 15-17, 22b, c, 23-28; 

 Plate 38, figs. 1-7) have a straight conic rhabdome, 2.3-3.2 mm. long and, at the 

 cladome, 64-85 n thick. A little below it is usually somewhat thickened and 

 here measures 65-89 n in transverse diameter. This thickest part of the rhabd- 

 ome is, on an average, about 6 % thicker than its ciadomal end. The acla- 



