42 A NEW METHOD FOR GROWING HYDROIDS IN SMALL AQUARIA 



great rate, sending out lateral stolons and quickly producing large 

 hydranths. 



A most fascinating and beautiful sight was to see the colony at night 

 under a low-power lens, illuminated by a strong light against a black 

 background, and to watch the fate of the copepods as they passed 

 down the tube. Usually the copepods on entering the tube either 

 were carried clear of the colony, or going among the hydranths 

 succeeded in escaping into the narrow tube, and then were rapidly 

 ejected along with the air-bubbles. As the current through the tube was 

 fast enough to pass the whole of the water in the bell-jar through 

 several times during the day, the copepods, which escaped on their 

 first round were liable to a few more passages of the tube, until 

 their fate was settled by the hydranths which had recently emptied 

 their stomachs. 



On watching the copepods passing through the tube, it was clearly 

 seen how a steady, continuous current in one direction was of advan- 

 tage to the hydranth in securing a copepod. A copepod would be 

 seen to drift on to the expanded tentacles. If at the moment of 

 touching the copepod gave a jump it usually got away, but occasionally 

 the jump was delayed too long, and pressed by the current against 

 the tentacles, it remained just long enough to be secured. 



As my stay at the Laboratory terminated on November 17th, I was 

 only able to watch the growth of the colony for eleven days, and 

 during that period the new growth far surpassed that of any Bo^ujain- 

 villia which I had previously tried to grow. Mr. L. R. Crawshay most 

 kindly took charge of the colony, and I am able to give a further 

 account of the growth from his letters to me. 



Letter dated November 30th : — " The colony has been kept well fed 

 with copepods every day. The air-pump continues to work success- 

 fully, so that the food supply has been continuous. The growth of 

 the colony has consequently been very rapid, more especially, or 

 almost entirely, over the basal stolon, which by yesterday had 

 extended over the whole length of the tube, lining the main expanse 

 of the interior surface. Young polypes have grown out from this 

 surface at every part, and almost without exception at or near the 

 points where branching of the stolon occurs. But so far as I have 

 observed the polypes are simple; there is no tendency to a tree- 

 like expansion anywhere. The parent part of the colony has not 

 developed." 



" The colony has developed enemies ; from what source I know not, 

 whether from veligers in the tow-nettings or from original infection. 

 Three days ago three minute nudibranchs were first observed browsing 

 on the hydranths, which proved to be Tcrgipes despedus. Yesterday 



