FORM OF A SPONGE 



295 



L. as peril of Text-fig. 1 was 7 cm. a second, and this was the 

 basis adopted in the calculations of this paper. I have now 

 changed them, in consequence of the conclusion that the actual 

 mean oscular ^•elocity when the sponge was in the sea was 

 8-5 cm. a second (Appendix, Note 1).^ From Parker's experi- 



Text-fig. 2. 



^.. 



ments on the pressure in Stylo tell a, a siliceous sponge, 

 its velocity is considerably higher than that of Leucandra; 

 we shall see later that this could be conjectured from its 

 structure." 



In quite still w^ater such a current from Leucandra goes 



^ This was the conchision from observations of length of jet and velocity ; 

 I cannot put it forward as an exact i)hysical measurement, but as a final 

 judgement after considering ui^wards of 1,000 unsatisfactory and imper- 

 fect observations, of the nature described in the text. Note 6 (Appendix) 

 indicates that the figure 8-5 was a lucky judgement, and is probably close 

 to the true velocity. 



- The velocity in Stylo tella will be less than Parker calculates^ 

 as he does not allow for the friction in the canals of the sponge. 



NO. 266 X 



