TOILERS IN THE SEA. 



spicules, and with papillae of the same size, number, 

 and arrangement, are always found to branch and 

 to anastomose in a similar manner, and to have the 

 terminal twigs of the same character. This surely 

 could not happen, did Cliona take up its abode in 

 cavities caused by decay, or in excavations formed by 

 worms, and were its shape dependent upon such acci- 

 dental circumstances." The prevailing belief, at that 

 time was, " that Cliona does not excavate the chambers 

 in which it is found ; but that they are formed by 

 worms, or by decay, or are produced in some other 

 accidental manner, and that the shape of the sponge 

 depends on that of the cavities it may chance to 

 inhabit." In opposition to which, he continues, " It 

 is pretty evident that they must form their own 

 habitation," and this he illustrates by reference to a 

 particular species, in which " the principal stems 

 take a zigzag direction, sending off at the angles 

 lateral branches, which pass on to unite with the 

 neighbouring stems : the terminal twigs are delicate 

 and bifurcate, one of the divisions going immediately 

 to form its junction with the adjoining stem. This 

 mode of growth goes on, until the entire substance of 

 the shell, in which the Cliona is lodged, is completely 

 filled with a network of branches ; the anastomosing 

 increasing all the while, by the addition of twigs from 

 the main stems, until very little of the shell is left to 

 separate the various parts of the sponge. Now, in 



