PORIFERA. I. 



53 



The skrlffou consists of a chiefly unispicular network the meshes of which are triangular, or, 

 to put it more exactly, tetrahedral ; therefore there is no question of primary or secondary fibres. The 

 form of the ends of the spicules makes them to fit well into each other. In the nodes, in wliich, ac- 

 cording to the construction of the .skeleton of tetrahedral meshes, a greater number of spicules meet, 

 these spicules are united by a very small amount of exceedingly clear spongin which is difficult to 

 observe. 



Spiciila are spined strongyla (acanthostrongyla) of a peculiar form; they are of equal thickness 

 in their whole length, and have rounded ends; the ends are bent rather suddenly to a more or less 

 high degree; they ma}- both be bent in one direction, or in opposite directions in the same plan, 

 and the}- may finally be bent in different plans. Sometimes the bending is minimal. The\- are set 

 with small, scattered spines, only the ends are smooth. The length varies between o'2o8— 0-238'""', which 

 agrees with the measure given by Carter, I.e., viz. about so^o^ginch =0-211""". The thickness varies 

 between 0-010—0-012""'. Finer spicules, developmental forms, occur in small numbers; these spicules 

 are of interest as furnishing a distinct proof that the spicules are begun in full length; the fact is 

 that the finest are of the same length as the fully developed ones, so that a growth only takes places 

 as to thickness; the finest are of quite the same form as the fully developed ones, but are quite 

 smooth, while the somewhat thicker ones begin to get quite minute spines; accordingly the spines 

 appear first during the growth. 



To get a clear understanding of the growth of the spicules, it is of importance 

 here to notice that the spicules of this species, which during the growth onh- increase 

 in length to a very slight degree, are strongyla; a laying on of new parts parallel to 

 the surface of the spicule will only lengthen such a spicule to an almost impercep- 

 tible degree. The fact vill be quite different when the question is of long tapering 

 spicules as oxea; in these spicules a laying on of parallel layers will lengthen the 

 spicule considerably, so that a spicule growing to the double thickness, may also 

 reach about the double length. The annexed sketch illustrates as an example the 

 difference in the increasing of length in strongyla and oxea. Developmental forms 

 of oxea, therefore, are always more or less shorter than the fully developed needles. 

 When, what is often the case, the ends of the spicule during the development become 

 more shortly tapering, than they are in the younger forms, the increasing of length 

 is also comparatively smaher. 



Locality: We have five specimens of this characteristic species; east of Iceland, 64° 07' Lat. N., 

 11° 41' Long. W., depth 168 fathoms, two specimens (Wandel); Ingolf, the Denmark Strait, station 89, 

 64° 45' Lat. N., 27' 20' Long. W., depth 310 fathoms, three specimens. 



Grogr. distr. Of this species only one specimen had been taken before by the Porcupine. - 

 expedition 1870, station 25, 37° 11' Lat. N., 9° 07' Long. W., close to the north of cape St. Vincent, depth 

 374 fathoms (Carter, I.e.). According to Topsent (Eponges nouvelles des Azores. Mem. de la Soc. 

 Zool. XI, 1S98, 226), it was taken during the cruise of Princesse-Alice > 1895—97 at the Azores. 



The genus Mctscknikozuia now, after the addition of this interesting species, counts, as far as I 

 am able to see, five species in all; of the other four species the three, tuber culata Grimm, intermedia 





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