REPORT ON THE HEXACTINELLIDA. 79 



Strassburg. Including the basal tuft this form lias a leugth of 20 cm. The portion 

 which projects freely from the mud is 12 cm. in length, and its cross section is oval, the 

 long axis below measuring 35 mm., but above, just below tlie dome-like arched sieve- 

 plate, only 25 mm.; the short axis beneath measures 30 mm., and above 22 mm. A 

 compai'ison of these figures wdth those recorded by Marshall for his specimen, shows that 

 we have here to deal with a I'elatively small, and probably young specimen. In form 

 it agrees throughout with Marshall's sketch and figure,^ exhilnting a straight tube 

 whose diameter is greatest somewhat beneath the inferior third part, and diminishing 

 upwards at first very gradually, finally somewhat more rapidly, becoming narrowest 

 just beneath the terminal sieve-plate. Both cuff and external ledges are entirely 

 absent. The inferior extremity is continued with a more gradual narrowing into the 

 long, soft, hair-like basal tuft. 



The arrangement of the round parietal gaps, which are almost 1 mm. in diameter, in 

 regular, transverse and longitudinal rows is very manifest. Between these parietal gaps, 

 which lie in pit-like depressions, a rectangular lattice-work of transverse and longitu- 

 dinal elevations projects both in the outer and inner surfaces (PI. VI. fig. 1). A 

 system of rectangularly crossed longitudinal and transverse bands of fibres, of which the 

 latter project most internally, while the former cross them transversely on their outer 

 side, serves for the support of this lattice-work, which forms somewhat narrower meshes 

 at the upper than at the lower end. Transverse fibres also occur, and these become 

 interwoven with the system of longitudinal fibres, sometimes occurring above, and some- 

 times beneath the latter. The longitudinal and the transverse bands of fibres do not 

 always form, as in Euplectella aspergillum, simple and compact bundles, but frequently 

 consist of two separate, but parallel bundles which lie close together, or at some distance 

 from one another. Llarshall describes these double bands of fibres as somewhat constant 

 and characteristic of the species. In the specimens before me the division only occurs 

 here and there, and is most marked in the longitudinal bundles (PI. VI. fig. 1 ). The 

 circular fibrous bands exhibit this peculiarity only in the upper region of the sponge. 

 I believe, however, that this peculiar condition of the bands of fibres is of essential 

 importance for the characteristic architecture of the sponge, and especially for the 

 nature and method of its growth. Since the spicules do not here become firmly bound 

 to each other, the elements of each individual band of fibres may readily become 

 laterally separated. If this occurs in every two parallel bundles by a simple division 

 both of the longitudinal and circular bands, perfectly simdar new rows of quadrate 

 meshes become formed, which are ari-anged strictly in longitudinal and transverse 

 directions. A few particularly strong fibres always lie in the axis of each of these 

 longitudinal and transverse bundles of fibres. These are the much prolonged rays of 

 those strong tetracts whose axial cross corresponds exactly to the intersections of the 



1 Loc. cit., pL xii. fig. D. 



