8 SCIENCE PROGRESS 



and his results certainly seem to afford good grounds for refusing 

 implicitly to accept the accuracy of the views commonly taught. 

 He was able to keep the animal in an aquarium for six months 

 without any visible food. During this time its weight decreased, 

 and it was easy to ascertain, from a knowledge of the com- 

 position of the body, and from the weight of the latter at the 

 beginning and end of the experiment, how much carbon, etc., 

 had disappeared — that is, had been given off to the medium. 



Putter also estimated the average rate of exchange of oxygen, 

 carbon, and nitrogen during the period of "starvation." The 

 chemical methods employed appear to me to be quite sound. 1 

 Oxygen was estimated by the volumetric method involving the 

 oxidation of manganous to manganic chloride. Carbon dioxide 

 in solution was estimated by boiling the water sample in the 

 presence of acid and in a stream of C0 2 -free air, the gas 

 being afterwards absorbed and weighed. The total carbon was 

 determined by oxidising the water sample by potassium dichro- 

 mate and sulphuric acid. The CO thus formed was oxidised to 

 C0 2 by passing it over glowing copper oxide, and the latter gas 

 was absorbed and weighed. Nitrogenous substances were 

 estimated by Kjeldahl's method ; or by simple distillation of the 

 water sample, when volatile bases were obtained ; and by the 

 usual methods for the determination of nitrates, nitrites and 

 ammonia compounds. Putter thus estimated the rate of exchange 

 during the period of " starvation." The average loss of carbon 

 during this period, estimated from the loss of weight of the 

 animal, was o - oi55 mg. per animal per hour. But, nevertheless, 

 the actual amount of carbon given off by Cucumaria during 

 the same six months was no less than o*2 mg. per animal per 

 hour — that is, more than ten times as much as the loss due to 

 the decrease of weight during the " starvation." 



A sponge is an organism which displays but little differentia- 

 tion of tissues. It is strictly sedentary, and the only movements 

 which may be observed to be carried out by it are insignificant 

 contractions of the oscula. It possesses no prehensile organs, 

 and it obtains its food in an automatic manner from the current 

 of water which circulates through its system of cavities. 

 Although presenting very great modifications in arrangement 

 this system is essentially similar in all sponges : there is an 

 inhalent system of openings, an exhalent system, and a series of 



1 Vergl. Phys. Stoftw. p. 6. 



