BY MEANS OF A CONTINUOUS CURKENT TUBE. 43 



the number had increased to six, and now the survival of the colony 

 is threatened by about thirty capsules of their spawn deposited all 

 over it." 



Letter dated December 18th : — " Shortly after my last letter to you, 

 a day or two only, it was evident to me that the six Tergi'pcs were 

 having it all their own way. They had stripped the whole stolon 

 area of almost every visible polype, and had, moreover, simply 

 plastered the same with spawn, containing, I should say, thousands 

 of their embryos. I therefore took out the tube and removed the 

 Tergipcs, and thoroughly cleaned out the bell-jar before returning the 

 Hydroid colony. The effect was very marked. In about two days 

 the polypes sprung up again in all directions, and the stolon con- 

 tinued to form a closer network inside the tube. But it is even now 

 to all intents and purposes a creeping colony. The first show of 

 arborescent growth occurred inside the tube. This happened after the 

 stolon had reached the summit of the tube and ramified over the 

 edge. A few days ago a similar branching growth appeared outside 

 the tube at one spot. But this is quite insignificant, with only about 

 three polypes, and no more than 10 mm. in height." 



"A new source of obstruction has arisen in the form of a brown 

 diatom, which in the past few days has come to infest almost the 

 whole interior of the tube." 



Early in February, 1907, I heard that the colony was still alive, 

 but owing to the intermittent failure of the air-pump and the scarcity 

 of copepods the colony had not put forth much new growth. 



In March the growth of diatoms and a small alga {Edocarims) 

 inside the tube was slowly choking the colony. A few vegetarian 

 molluscs were placed on the tube to browse on the algaa. They did 

 more than was expected of them in cleansing the tube. Within a 

 fortnight of their introduction the encrusting mass of diatoms, etc. 

 lining the tube broke away in large flakes, perhaps due to a poison 

 secreted by the molluscs, and carried away at the same time the 

 stolons to such an extent that the whole colony was destroyed. 



The successful growing of Bougainvillia is not altogether due to the 

 advantages of the current-tube, but greatly also to the personal attention 

 which Mr. Crawshay bestowed upon the colony. I sincerely thank 

 him for the interesting letters from which he has allowed me to quote. 



I am also greatly indebted to Dr. Allen. It was during the pre- 

 liminary testing of his air-pump that the current-tube was designed. 

 He at once most generously gave me the use of the pump, and took 

 a very active interest in the starting of the apparatus and in the 

 welfare of the colony. 



