6o 



PORIFERA. II. 



copious, but white and clear mass of spongiu, which is most developed towards the base; in the 

 skeleton outside of the axis, on the other hand, no spongin seems to be present. 



Spicida: a. Megasclera are long, slender subtylostyli, sometimes styli. They are straight, or 

 slightly, most frequently somewhat irregularly curved. The head-end is only very slightly swollen, 

 the opposite end tapers evenly to a rather long point which is often somewhat more abruptly pointed 

 at the end. The needles are here of only one kind, and are the same in the stalk and in the other 

 skeleton, the only difference being that in the lower part of the stalk they become gradually shorter, 

 and the needles that here project and make the stalk shaggy are also short. These short needles are 

 generally more highly curved, and are most frequently styli without any head-swelling, but they cannot 

 be separated from the others as a particular kind. The length is between ca. 0-35 and o - 84 mm , but in 

 these measures are also included the needles occurring towards the base of the stalk; if the lower 

 part of the stalk is excluded the lower limit of the length may be put to about o - 5 mm , and in a spicula- 

 jDreparation in which no sample from the lower part of the stalk has purposely been added, the length 

 of the needles therefore will be found to be ca. 0-5 — o - 84' nm , and the shorter ones will only occur more 

 rarely. The thickness varies from ca. o - oo8 — o-oi4 m,n ; the longest ones are not the thickest. Finer, to quite 

 fine developmental forms are seen in small numbers, b. Microsclera ; these are of two forms, aniso- 

 chelse palmatse and forcipes. 1. The anisochelse are of a form characteristic of the subgenus; the 

 larger end is of a similar form as in the preceding subgenus; the alee are very large and reach far 

 down, quite down to the lower end, and there is a considerably shorter and narrower tooth. The 

 smaller end is of a peculiar structure, not easily understood. When the chela is lying on the side a 

 pair of small points are seen at this end, one at the outer end of the axis, the other a little higher 

 up. The best view is got when the chela is seen in such a way as to turn the smaller end directly 

 towards the beholder (PL XI, fig. 4d), and then it is seen that alse and tooth are present as usual. The 

 peculiar feature is that the alae do not run along the shaft in the common way, but are placed almost 

 transversely on it. The axis then continues with a slight bend, and at the end of it the tooth is 

 placed parallel to the alse; it has a distinct tuberculum. When the alse and the tooth are seen from 

 the side, they are seen as the mentioned two points. When the chela is viewed from the front under 

 sufficiently high magnifying powers, a pair of refractive ridges are seen about where the alae of the 

 upper end cease; these ridges are the upper part of the alae of the lower end where they go off from 

 the axis ; they are here the most narrow, but downward they become gradually broader, and fold round 

 on the side; the whole thing might be described by saying that the upper outer corner of the ala had 

 been cut away by a large cutting rounded inward. The tooth, which is also somewhat curved, has a 

 form corresponding to that of the alse, being also most narrow above, but increasing in breadth down- 

 wards, and thus showing the same cutting. The folded sides of the alse and the tooth meet on the 

 side leaving only a narrow opening between them ; as a consequence of the form the lateral edges are 

 here short. The described form of the alae and the tooth, together with their position with regard to 

 the axis, is the cause why they appear as two points when viewed from the side under small magni- 

 fying powers. The anisochelse are 0-022 — o-025 mm long 1 ) and ca. o , oi2 in,n broad. Developmental stages 



') A few chelae were seen of a length of o-oi4 mm , but they, no doubt, belong to the embryos present in the sponge, see 

 below under Embryos. 



