Hints for Microscopy. 439 



and the lohole sac, with its oral and anal apertures, so far like 

 an Ascidian ; while the sac with its pavement-lining of cells 

 in the compound timicated animal goes on unan-ested to pro- 

 duce an Ascidian. It is on this account that I have stated 

 that there is a greater relation between the Sponges and the 

 Ascidians than between the Sponges and the Corals, whose 

 polypes have but one aperture for both pui-poses. 



To produce the "adaptation" there must be, of course, a 

 creative or directing power, which, being infinite^ we can 

 never comprehend. 



I would here add, for the information of those who care to 

 experimentalize on the Kving sponges by feeding them with 

 indigo or carmine (magenta will not do, for it dyes all alike), 

 that the portion of sponge must be taken from its habitat 

 without injiuy, put in sea-water directly, kept there until 

 the following day (forenoon) ; the water then changed, and 

 the indigo or carmine added by having been rubbed off a 

 cake of one or other of these substances in sea-water, and 

 di'opped upon the sponges, where it should be allowed to re- 

 main about an hour, always remembering that the experiment 

 will be unsuccessful if it be not previously ascertained, by the 

 ejection of particles from the vents (which can be seen under a 

 1-inch compound power), that the sponge is living and active. 

 Portions may then be examined microscopically, after which 

 the sponge should be placed in spirit and water for doing this 

 at convenience. 



A priori it might be considered desirable to have the sponge 

 as fresh as possible ; but experiment has taught me otherwise, 

 viz. that to get the cilia retained with the indigo still in the 

 body of the spongozoon, the sponge should be kept for a day 

 first, in the way above stated, whereby, being weakened and 

 hungry perhaps, the experiment is more likely to succeed. 



Then, of course, the best plan is to examine a portion while 

 the sponge is yet alive] after which it may be placed, as 

 above noticed, in spirit and water for more deliberate obser- 

 vation. In this state, too, a portion may be torn to pieces 

 on the slide, dried and mounted in balsam, when, in many 

 instances, the general form of tlie body and cilium will still 

 be retained ; or the fragments may be dyed with magenta, 

 when the cilium will become still more evident ; but, of 

 course, wha,t will render the transparent sarcode visible, 

 will be likely to obscure the particles of indigo. Lastly a 

 fragment having been torn to pieces on the slide in water, it 

 may be simply di'icd, wlien tlic cilium will become more 

 evident than in the wet state. 



