THE SPOXGIDA OR PORIFERA. 339 



There can be no doubt that the wide differences of opinion 

 regarding the " nature and affinities of the Sponges," result, in a 

 great degree, from the difficulty attending accurate and continued 

 observations and study of minute living forms, such as the 

 Infusoria, and the Flagellate and other cells which play so 

 important a part in the life-history of the Sponges. It will be 

 necessary to allude later on to this matter, and also to some of 

 the arguments adduced by Saville Kent. At present we feel dis- 

 posed 'to suggest that some of those interested in Biology, who 

 have difficulty in determining the particular group of living forms 

 on which to devote special attention, may — with advantage to 

 themselves, and possibly to science — select the Spongida as a 

 speciality. There can be no lack of material to work upon. 

 There is the fresh-water Spongilla, and numerous marine species 

 are found in abundance on the British coasts. In these days of 

 the parcel post, living specimens can be easily and successfully 

 transmitted in sea-water from seaside resorts to inland counties. 

 We have often received Sponges, alive and vigorous, from the 

 Channel Islands by means of the parcel post. This is a highly 

 important matter, for it is not sufficient to examine only the 

 general conformation, the spicules, the canal system, the dried or 

 preserved fabrics of different species of the Spongida. Every 

 effort should be made to obtain as many species living as possible, 

 so that the vital elements of the Sponge, the flagellate collared 

 cells, the amoemibiform cells, the "ciliated larva," or gastrula, may 

 be studied as minutely as possible. 



Considerable practical experience in working with the micro- 

 scope, the preparation of slides, and the use of very powerful 

 objectives, will be required in the pursuit of such a study. Saville 

 Kent, when investigating the Infusoria, adopted means of pursuing 

 his researches which those who propose to study minute living 

 forms would do well to imitate. Instead of the usual " cover- 

 glass," talc — such as is used for glass shades — is recommended. 

 This may be readily split into scales of exceeding lightness, trans- 

 parency, evenness, and thinness ; and such scales can be easily 

 cut with scissors, and bend so easily that objectives may be racked 

 close down on the objects to be examined. It is stated that with 

 such thin talc covers, the use of i/i6th, 1/2 5th, and i/5oth inch 

 objectives becomes comparatively an easy matter. 



