BY E. P. HALLMANK. , 455 



compact solid mass, or lieail, with di^itiform protuberances 

 (PI. xxi., fig.5); occasionally, in the case of T. reteporoniif<, the 

 sponge may remain unbranched — consisting simply of a long and 

 slender, undivided stem. According to the species (or variety), 

 the branches may be either cylindrical, distally expanded {i.e., 

 more or less clavate), or gradually tapered. Anastomosis between 

 the branches occurs to a greater or less extent almost invariably, 

 except perhaps in the case of T. retepurunns. The mode of 

 branching is probably never dichotomous, thougli occasionally it 

 may appear so; normally at any rate, the bi'anches arise laterally 

 and fidventitiously. 



The oscula are of small size, very seldom as much as 1 mm. in 

 diameter, and are generally sca'ttered over the surface irregularly; 

 in T. rctt'iiornsns, however, they show a decided tendency to l)e 

 arranged in longitudinal series, especially along the edges of the 

 bi-anches when these are compressed. In T. piLstidosii^, the 

 oscula are restricted almost entirely to the distal pai'ts of the 

 branches, while in T. hactrviimb they are said to occur arranged 

 in groups. 



The surface is smooth, or is provided with numerous minute 

 prominences (up-pushings of the dermal layer) produced by the 

 extremities of impinging skeletal fil)res. These elevations con- 

 stitute a marked featui'e of the surface only in T. p\tstulos7is (and 

 T. hacteriuin I) in which they have the appearance of small 

 pimples, and in T. acabrusus (PI. xxi., fig.4; PI. xxviii., fig.6), ir, 

 which they take the form of minute sharp conuli; in the remain- 

 ing species, they are either imperceptible or produce merely the 

 appearance of granulation. In any case, whether surface-eleva- 

 tions occur or not, each point on the surface at the extremity of 

 a skeletal fibre is the location of a small ai'ea over which the 

 dei'mal membrane is adherent to the underlying tissues and free 

 from dermal pores, whilst elsewhere it overlies subdermal spaces 

 and is perforated by numerous pores. The pores are either 

 scattered singly and for the most part subequidistantly, at an 

 average distance apart not much exceeding their own diameter, 

 as, for example, in T. di<jitatus and its varieties (Pis. xxvi., xxviii.); 



