47 



prehend that it can need no detail of argument or mathematical 

 demonstration to show, that upon the mode and degree of fold- 

 ing of this membrane, the greater or less freedom of access, 

 change, and circulation of the water, and its consequent power 

 of being acted upon by the numerous ciliated tentacles and move- 

 able processes, must have depended. Every one who is familiar 

 with the difference in mere circulation of air between the narrow 

 street and the open road, between the deep valley and the hill 

 top, will recognise the essential importance in this respect of every 

 difference in that mode and degree of folding ; and, when the 

 extreme minuteness of the individuals is considered, it will appear 

 that variations of fold hardly appreciable to the eye will have 

 probably had a material influence on the condition of the tenants 

 of these wonderful structures. I cannot doubt that every con- 

 stant difference in the mode and degree of folding of the Ventri- 

 culitic membrane was accompanied by some modification in the 

 organs or habits of the animals, adapting them to that particular 

 mode and degree of access, change, and circulation of sea-water 

 which that mode and degree of folding made a matter of absolute 

 necessity*. 



Taking then the Ventriculidse as a family of the Polyzoa, I 

 shall first endeavour to show that there are certain broad and 

 very marked constant modifications in the mode of foldingf cha- 

 racterizing certain extensive groups which yet have many points 

 of constant difference between the individuals which, as groups, 

 are respectively thus characterized. These groups will form 

 distinct genera. I shall show that certain subordinate but yet 

 important modifications mark, in common, several of the indivi- 

 duals of each of these genera, which individuals yet have further 

 still subordinate but constant and therefore characteristic points 



* Sir J. G. Dalyell, in his recent work on ' Remarkable Animals of Scot- 

 land/ especially notices the importance of attention to the varying condition 

 of the water in which specimens are kept as the great secret of their preserva- 

 tion ; and even his care has often failed. A " low organization " and slight 

 sensibility have been hastily attributed to Polyzoa from their enduring great 

 changes of heat and cold. There is no animal capable of enduring greater 

 changes in this respect than man. But take another class, and it is well- 

 known that from the same heap of frozen fish one may be dashed to shivers 

 on the ground, while another, put into a pail of water, will, in two minutes, 

 be swimming about. 



f* The inquirer will at once perceive the difference between this and mere 

 external form. The same general external form may mask numberless most 

 different modes of folding. My object is to aid in realizing, by classifica- 

 tion, the living animal in all its integrity and varieties. By the accumu- 

 lated names Scyphia, Coscinopora, Guettardia, &c., nothing ever was or can 

 be vivified ; no real idea conveyed to the mind. But the object of the natu- 

 ralist should surely be, not an accumulation of mere names, but the realiza- 

 tion of living and true ideas of various absolute modes of actual existence, 

 be they past or present. 



