Sponge-fauna of Norwny. 449 



cases in Tetilla (Ann. & Mag. Nat. Hist. ser. 5, vol. ix. pi. vii. 



fig. 18). 



Sperm-balls (PI. XVII. fig. 28) are the last constituents of 

 the mesoderm to which we need allude ; they are rounded or 

 oval clusters measuring about 0-0071 inch along the minor, and 

 O'Ol inch along the major axis, consisting of a vast number of 

 closely packed spherical bodies of various sizes, from 0*00025 to 

 0"000057 inch in diameter. These stain deeply with carmine ; 

 they present no trace of flagella, and are probably spermatozoa 

 in an unripe state. Immediately surrounding each sperm- 

 ball the gelatinous matrix is very finely fibrillated, and outside 

 this thin fibrillar layer abounds in young abundantly and fre- 

 quently coarsely granular protoplasmic cells (PL XVII. fig. 

 1), which appear to be connective-tissue corpuscles, with 

 short branches and in a very active state of growth. The 

 large amcebiform cells are also sometimes found close to the 

 sperm-bail. Besides these, abundant fusiform connective- 

 tissue corpuscles radiate from the surrounding tissue to- 

 wards the sperm-cluster, and penetrate the fibrillar layer 

 which immediately surrounds it. This layer, when seen 

 from the inside by the removal of the sperm-granules, pre- 

 sents the appearance of very fine curved striaj, whicii wander 

 about in all directions, but exhibit a more or less concentric 

 direction about the ends of the fusiform corpuscles which they 

 surround (PI. XVII. fig. 16). 



Finding such a specialization of the mesoderm about each 

 sperm-ball, one almost expects to find them also characterizing 

 some special region of the body ; but this is not the case ; 

 they occur as near the top as the bottom of the sponge ; and 

 all one can say is that they do not approach nearer the surface 

 than the third vesicle of the incurrent system. 



Development. — On the early stages of development I can 

 contribute no information ; but Mr. Norman's specimens have 

 furnished me with six very young forms, which differ in several 

 particulars from the adult sponge. All six agree in having 

 a prolately ellijDsoidal body provided with a single anchoring 

 fibre ; and in none is there any trace of an equatorial recess. 

 This is also absent in Prof. Wright's specimen ; but in a little 

 example 0*5 inch broad by 0*4 inch high, with five rootlets, it is 

 perfectly developed, as also are all the other characters of the 

 adult sponge. The length of the body in the smallest speci- 

 men (PI. XVII. fig. 7) is 0-02 inch, in the largest O'OG inch. 

 The anchoring-fibre is continued through the centre of the 

 body as an axis ; and a tuft of spicules projecting from the 

 oscular end seems to be its upward termination. In the larger 

 specimens the tufts of spicules radiating from the oscular 



