STRUCTURE OF THE LARVA OF SPONGILLA LACUSTRIS. 437 



which line the bank of the river^ on logs of wood in the river, 

 and on the pillars which support the bridges. The sponges 

 were taken from the river in the early morning. The roots on 

 which they grew were cut, and the whole of each colony was 

 transferred from the water into a glass jar full of river water 

 in as complete a condition as possible, and taken into the 

 laboratory of the University Museum, where, through the 

 kindness of Professor E. Ray Lankester, this piece of work 

 was done. Great care was exercised so as not to leave the 

 mother sponge for any length of time out of water. The 

 sponges, having been brought into the laboratory, were placed 

 in glass vessels with wider openings than those in which they 

 were carried in. The vessels were then put in the tanks, and a 

 slow current of water was allowed to flow over them. In this 

 way as many larvse as was desirable could be collected. 



Owing to the continual supply of fresh water the sponge was 

 kept in an active and healthy condition. The oscula were 

 always open, and a stream of water could be seen to issue out 

 of them, carrying with it at intervals the larvae. The larvse 

 were almost invariably produced on the same day ^s the mother 

 sponge was taken from the river, often on the same morning. 

 The larvse appear to be carried helplessly out of the oscula by 

 the current, but in all cases they soon gain complete control 

 over their movements, and swim towards the surface. They 

 dart downwards instantly when disturbed. As they swam at 

 the surface they were easily caught with a pipette and removed 

 into watch-glasses. Some of the larvse so obtained were pre- 

 served at once, while others were reared in watch-glasses, allowed 

 to fix and to undergo metamorphosis, and were preserved at 

 various stages in their development. 



The watch-glasses in which the larvse were placed measured 

 about 18 cm. across, and were about two thirds full of river 

 water. The watch-glasses were first of all carefully cleaned 

 with strong hydrochloric acid and with ether successively. 

 They were then covered over with a thin layer of glycerine, 

 except for about half an inch near the edge, and finally with a 

 thin layer of paraffin of low melting-point. The glycerine 



