286 A MONOGRAPH OF THE AUSTRALIAN SPONGES, 



into the internal system of lacunifi. The development of this 

 lamella is subject to great variations. The pores are either round 

 and small or they are enlarged and become polygonal, Then only 

 narrow strips of tissue remain between them. Finally the pores 

 may attain the size of the lacunse below, when of course the 

 dermal lamella as such disappears altogether. (Plate XXVI.) 



The forms of the species Halme Nidus Vesparum, globosa, and 

 micropora possess a more or le.ss developed dermal membrane of 

 this kind, whilst such a structure was never observed in any 

 specimen of Halme simplex. 



The shape of the Halme specimens is very variable. Massive 

 forms and such with finger-shaped processes appear to be the most 

 frequent ones. Halme simplex is always expanded, flat and 

 incrusting. 



In the surface both of the covering lamella and also of the 

 lamellse in the interior, we meet with numerous small inhalent 

 pores of ellyptic shape, which are covered by a sieve-membrane. 

 These lead into short and wide cylindrical inhalent canals, v.diich 

 open into the common subdermal cavity. Irregular and short 

 pillars of tissue traverse the cavity and unite the skin with the 

 inner part of the body. There is no Pseudosculum, Halme is a 

 true Auloplegma. 



The subdermal cavity is low. From its inner surface inhalent 

 canals of irregular transverse section originate which branch in a 

 more or less penicillate manner. All these canals seem to tend 

 upwards. The final ramifications of the inhalent system are regular, 

 cylindrical canals with a circular transverse section. These canals 

 are comparatively very wide, as even the smallest have a diameter 

 greatly exceeding that of the membranes of tissue which separate 

 the two canal sytems. 



The exhalent cantils are wider than the inhalent ones. They 

 commence with sack-shaped cylindrical branches, uniting like- 

 wise in a penicillate fashion to form the larger exhalent stems. 

 The canals become more and more irregular the larger they get, 

 and finally appear as irregular and wide lacunae. The osculum is 



