Studies on Spoüges. 439 



the exhalant canals. The Chambers that are found just imder the sub- 

 dermal cavities receive the water directly from these (fig. 4 s.d.c.) ; 

 they communicate by pores. Those which He more towards the ceutre 

 receive the water by the inhalant canals (fig. 4 i.e.). Around the 

 more or less cylindrical afferent or exhalant canals they are radially 

 arranged and over the whole length; transverse and longitudinal section 

 will make this clearly ; both are to be Seen in fig. 4. Although typically 

 they are poiich-shaped and open with a wide mouth directly into the 

 canals, there are modifications of this form that remind us of the system 

 of other Sponges. In figs. 5—9 I have drawn diflferent shapes of cilia- 

 ted Chambers. In fig. 6 and 8 there are some that resemble those of 

 the Sjìongidae, showing even the beginning of a special afferent canal. 

 It must however not be forgotten that these forms are exceptions and that 

 in general they are pouch-shaped as in Spongelia. As regards the 

 number of the pores this seems to be very variable. The maximum I 

 saw on thick sections was 12, so that in all, one Chamber may have 

 more than 20 pores. 



Although very often it may appear that exhalant canals also function 

 as inhalant, this seems to be an error. Numerous complete series of sections 

 showed me that the inhalant canals in the innermost parts of the body never 

 communicate with exhalant ones, but always came from other inhalant 

 ones. So I believe that the water, once having passed a ciliated 

 Chamber, does not enter another , but is carri ed away. 



Thus we have in Velmea as usuai two Systems of ramifyiug canals 

 lying rather close together and in communication by ciliated Chambers. 



Each branch of the Sponge-colony is a more or less cylindrical 

 tube, the canal in the middle of which we may cali the cloacal cavity. 

 In this cloacal cavity ali the excurrent canals open. The diameter of 

 the cavity is not everywhere the same; and there is present an ar- 

 rangement for altering the size of the lumen. In observing a tube from 

 the top, very often a thin membrane with a circular hole is visible ; it 

 is highly probable that this membrane works as a sphincter. The cloa- 

 cal cavity is partly fiUed up bere and there by a spongeous mass, as is 

 to be seen in figs. 19 and 21. In this whitish soft substance are no 

 skeleton-fibres ; the whole mass consists only of connective tissue. 



Velmea has a very remarkable skeleton. It consists of a rather 

 regulär network of horny fibres, which lie in the three dimensions of 

 space. On transverse sections it is to be seen that one system of fibres 

 passes in a radiai direction, while another is a system of concentric 

 fibres. At the place, where they unite, the longitudinal fibres come 



29* 



