198 PROJECTS FOR THE IMPROVEMENT OF SPOXGE-FISHERIES. 



would SOW themselves naturally on the tiles, renderiug cuttings un- 

 necessary. 



It would be better if the hurdles were sunk rather in deeper water 

 than that from which the sponges are taken, lest the cuttings should 

 suffer from excess of light, I should cut the sponges in a wooden 

 trough, holding enough water to cover the sponge. The advantages 

 expected by the method would be : — 



(1) Increase of the bearing area of the field. 



(2) Eemoval of the sponges witliout injury, and with careful 



selection. 



(3) Increase in the rate of growth, and in the maximum size. 



(4) Improvement in shape of the sponges. 



There is also a proposition given by Dr. von Marenzeller which 

 deserves attention. Larger sponges are naturally of greater value, in 

 proportion to their weight, than smaller sponges; and he points out 

 that if two or three be attached closely together (misshapen specimens 

 could be thus utilized) they will grow into one sponge. 



In this case, also, I should suggest the use of the needle and thread to 

 effect the attachment; and, from the biological point of view, there is 

 little doubt of effectual union. But the possible existence of biological 

 disadvantage, in total ultimate weight, cannot be estimated until we have 

 some knowledge of the laws of growth in sponges ; and the commercial 

 advantage depends not only on this, but on market details, as to which 

 I cannot find information. Probably the increase in value with size of 

 Nassau sponges is far less than with those of the Adriatic. 



It must be understood that these recommendations are based princi- 

 pally on general reasoning from what is known of the conditions of life 

 in sponges. The direct experimental evidence bearing on the questions 

 involved is slight, imperfect, and uncertain ; the work done by Professor 

 0. Schmidt (6) was brilliant ; but it has remained incomplete, as he left 

 it, for twenty-three years. 



To avoid needless waste of capital, it is desirable to make a series 

 of exact observations on the sponge of commerce with regard to the 

 following points : — • 



(1) Rate of growth, and length of life, of sponges growing naturally 



on the sea-bottom. 



(2) Do. do. of sponges attached with their natural bases to artificial 



trestles or hurdles. 



(3) Do. do. of sponges raised from cuttings in either position. 



(4) The size at which, in self-sown sponges and in cuttings, breeding 



commences. 



