PORIFERA. III. 



The fully developed tylotes have about equal ends, but single developmental stages were seen, distinctly 

 showing, that the tylote originally is monaetinal. b. Microsclera; there is only one form, rh aphides; 

 they have the special shape which is probably common to all the rhaphides in the species of Tcdania. 

 One end is short and curiously, obliquely pointed, while the other end tapers into a long, very fine 

 apex; otherwise they are spinulous which under a low magnification is only seen as an indistinct fine creuu- 

 lation; under a greater magnifying power it is on the contrary seen, that they are distinctly spined, the spines 

 being dentiform and strongly compressed in the longitudinal direction; the smaller rhaphides are the 

 relatively most strongly spined (PI. IV fig. i c). The length varies to a very high degree in the 

 single individual, and also somewhat from individual to individual; it is in all 0-053— 0-50™™, gen- 

 erally it is o-o6o— 0-32 mm . Whether these different sizes are developmental stages it is difficult to de- 

 cide, but it is most probable, that they are, at all events for a great part, fully developed forms. To 

 be sure all intermediate sizes are seen between the given sizes, but certain sizes seem to predominate 

 and I am inclined to think, that three different, independent sizes are present (PI. IV fig. 1 c). When 

 intermediate sizes are found between them, this may be due partly to the variation of the single 

 sizes, but perhaps also partly to the fact, that a number of developmental stages are present among 

 them. The thickness is, in relation to the length, about o-ooio— 0-0028 mm ; the latter thickness was 

 only reached by the longest rhaphides and consequently not found in all individuals. The rhaphides 

 occur in great multitude both in the dermis, and otherwise in the tissue of the sponge; they occur 

 both in dragmata and singly and scattered; I have however only seen the large rhaphides in drag- 

 mata; all rhaphides in a bundle seem to have the equal ends turned in the same direction. 



To show the variation in the length of the different spicules in various individuals and how 

 the lengths with regard to all three forms of spicules are in the main related to each other I may 

 give some measurements: 



Styles tylotes rhapides 



0-30— o'35 mm 0-25— 0-32 mm °'°55 — °' 2 5 '"'" (small specimen). 



0-35— 0-47 m,n 0-27— 0-33 mm 0-053— 0-29 mm 



0-44 — o-49 mm 0-31 — o - 38 mm 0-064— o-32o mm 



0-43 — 0-53 mra 0-35— 0-41 ,nm 0-064 — o'329 ,nm 



0-51— o-68 mm 0-35— 0-47 m,n 0-064— 0-50""" 



Remarks: As Schmidt's type-specimen is found in my material, the identification is certain. I 



have also examined a type-specimen of Tcdania increscens O. Schmidt, and have thus been able to 



decide with certainty, that this species is identical with suctoria. Thiele thinks 1. c. that increscens 



might be a good species, because its styles are larger than the measurements given by Schmidt for 



suctoria; but the variations of the spicules given above show however, that from this no character can 



be drawn. Tops en t himself (Rev. Suisse de Zool. IV, 1897, 454) has abolished Tcdania conuligera as 



identical with suctoria, and his description also shows, that this is correct. The specific characters for 



the species of Tcdania seem especially to lie in the shape of the dermal tylotes, and this is not 



astonishing, as the dermal spicules in other Myxillem are also characteristic. Besides T. suctoria I 



have examined T. digitata O. Schmidt, tcnuicapitata Ridl. and massa R. and D., and of these species I 



have examined specimens of suctoria from the whole Ingolf territory and from the Willem Barents 



