and Functions of the Sponge. 1S5 



them to seek and to take that vertical position which seems ne- 

 cessary to their future development ; and, by this locomotive 

 power, produced by the vibrations of the ciHae, the ova are sus- 

 pended for a longer period at the mercy of the waves, the tides, 

 and the streams of the ocean, by which the species are gradual- 

 ly spread over the globe. Thus the S. communis, S, lacinulo- 

 sa, S. usitatissima, and other horny species, which seem to be 

 confined to warm climates, and abound in the Red Sea and the 

 Indian ocean, appear to have been gradually wafted by the Gulf 

 Stream from the shores of the east to corresponding latitudes 

 of the new world. The S.Julva, S. fistularis and fine varieties 

 of the S. officinalis. Pall, are among the horny species which 

 abound on the tropical shores of America, and their elastic fila- 

 ments form a beautiful transition to the cartilaginous threads 

 which wind round the cells of Alcyonia. All the known calca- 

 reous sponges are inhabitants of the British coasts ; the delicate 

 and minute S. compressa has been seen on the shores of Greenland, 

 Shetland, Scotland and England, and I have found it along with 

 the S. nivea abundant and extensively distributed over the West- 

 ern Islands. The S, hotryoides, S. nivea, and S. compressa, are 

 calcarious species, inhabiting the Frith of Forth. An immense 

 number of silicious species inhabit our northern latitudes ; and 

 from their peculiar habits, their simple structure, and their te- 

 nacity of life, they are probably the animals which exist nearest 

 to the poles. The S. coalita, S. oculata, S. dichotoma, S. pro- 

 lifera, S. palmata, S. suherica, S. papillaris , S. panicea, S. cris- 

 tata, S. tomentosa, and S. cinerea, Gr., (fig. 8«) are found in the 

 Frith of Forth. The ^S*. papillaris and S. tomentosa I have 

 found common on the coasts of Britain, Ireland, and the West- 

 ern Islands ; and I have observed the aS'. panicea roofing the ex- 

 cavated basaltic cliffs of the island of StafFa. The S. sanguinea^ 

 Gr., (fig. 9.) a remarkable blood-red sessile species, I have found 

 growing, like the S. panicea, on the under surface of the sea- 

 beaten rocks of Islay, StafFa, lona, and, along with the S. ni- 

 vea, at the entrance of the spar caves on the shores pf Skye. 

 The S. tomentosa is said to occur on the shores of Europe, 

 North America, Africa and India (Lamouroux, Hist, des Po- 

 lyp, p. 30.) ; but I believe it has not been authentically she^vn 

 that the same silicious species occur in the corresponding lati- 



