ON TUE ZOOLOGICAL STATION AT NAPLES. 367 



water flowed. At first they seemed to thrive exceedingly well, but later 

 on they became very sluggish and hardly ever extended themselves. 

 Whether this was owing to the time of year, or to the weather, which 

 was exceptionally cold for Naples, or whether it was due to my having 

 overcrowded my tanks, I am unable to say. 



Spovgicola Jigfularis, F. E. Schulze, inhabits several of the silicious 

 sponges, but most of my work has been on specimens inhabiting either 

 Esperia hauriana, O.S., or 'Esperta Loren-ii, O.S. In these two species, 

 so far as I can judge from the few specimens of each that I have as yet 

 been able to make sections of, although the internal anatomy is the same, 

 the form of growth is different. 



In E. haiu-iana the chitinous tubes are straight, and do not generally 

 project more than 1 mm. above the surface of the sponge, and are very 

 long, tapering as they go deeper into the sponge, till they join each other, 

 forming a network. In E. Lorenzil, on the other hand, the tubes are much 

 shorter, that is, they form a network inside the sponge considerably sooner, 

 and they project often 2 or 3 mm. or even more above the surface, andai-e 

 generally curved. This may be due to their being different species 

 inhabiting different sponges, or it may be due simply to the different form 

 of sponges they inhabit. For whereas E. hauriana is solid all the way 

 through, E. Lorenzii is hollow, and therefore of course the tubes would be 

 obliged to become curved and to join each other nearer the surface. I 

 myself incline to the latter view, and I am also far from sure that when 

 the Monactinellid group of sponges are thoroughly worked through it will 

 not be found that E. lauriana and E. Lorenzii are the same species living 

 under different conditions. 



I have not studied these forms very closely, but from sections I have 

 of them (cut always for the purpose of obtaining sections of the enclosed 

 Spongicola) the anatomy of the two seems to me almost identical, as are 

 also their spicules. 



Coming next to my methods of examining and killing my specimens, 

 the chief difficulty arose from the extreme shyness of these animals, as 

 they will only extend themselves under the most favourable circumstances, 

 and the slightest movement is suQicient to cause the whole colony to dis- 

 appear again within their tubes. To examine them alive under anything 

 like a high power is almost an impossibility. The slightest jar of the 

 glass containing them, or of the table, almost invariably causes the instant 

 disappearance of every tentacular crown in the colony. 



I have often known them retract with nothing more than the jar 

 caused by the lens entering the water in which they were lying. 



When first taken from the aquaria in the morning, my specimens, 

 which I placed in glass boxes about two inches in diameter and one in 

 depth, full of water, would generally extend in from half an hour to an 

 hour, but if they again retracted they usually took much longer, and fre- 

 quently refused to extend themselves at all until they were again placed 

 in running water. 



The opacity of the sponge is another source of difficulty. 



Owing also to the fact of the Spoiujicola tentacles being white against 

 the opaque and also light-coloured background of the sponge, it is almost 

 impossible to make out even the number of the tentacles. 



With regard to killing them extended, I had practically no success 

 whatever. I have tried all the methods I could hear of, but with \evj 

 poor results indeed. 



