6 Mr. H. J. Carter on the Anatomy 



which is being beaten upon almost unremittingly by boisterous 

 waves, frequently in the most tempestuous weather, is crowded 

 with various species of Spongida, but all more or less dwarfed 

 from such exposure. 



Besides marine there are also freshwater sponges ; and 

 these grow in tanks, lakes, and rivers, on rocks, branches and 

 roots of trees, and aquatic vegetation generally, where they 

 may be subject to be left uncovered and dry for several months 

 of the year. 



Forms that may be assumed by Sponges. 



The forms that may be assumed by sponges are very 

 numerous and very different, not only in the mass, but in the 

 individual ; since, although a species may be recognized by the 

 form which it generally assumes, yet it may assume other forms 

 so different that it would be hazardous to decide on this alone. 

 Still the old practice in the description of a sponge was to 

 deal with the form only ; nor can we do without it now ; but 

 the addition of the elementary composition, which came in 

 with the improvements of the microscope, has furnished us 

 with the means of correcting the mistakes to which this was 

 liable. Yet the absence in the Spongida of any expression 

 visible to the naked eye, as the flower on a plant or the calice 

 on a coral, will ever be commensurately disadvantageous in 

 the description of sponges. Indeed, as will be seen hereafter, 

 little is to be achieved without the aid of the microscope, 

 since, as before stated, the same species may assume different 

 forms, and unfortunately the same elementary composition 

 may also be accompanied by different forms, while, there being 

 certain classes of forms which appear to be evolved out of 

 each other, two species may assume the same form and there- 

 fore at last be only determinable by the microscope. 



All this shows that the form of sponges is not less Protean 

 than their soft parts will hereafter be found to be ; and hence 

 their study presents difficulties in the way of classification 

 and species-determination to which no other branch of natural 

 history is equally subject. 



As, however, the means of designating sponges was origi- 

 nally and necessarily restricted to their forms and the likenesses 

 they bore to some well-known objects, this means obtained con- 

 siderable development ; so that the following Table, although 

 a little differently arranged, presents very little new in this 

 way, and is intended to supply the student with the means 

 not only of determining, but of describing a sponge so far as 

 its general form may be concerned. 



