38 JOURNAL OF THE [February, 



into three great groups, according to the substance which makes 

 up the skeleton. If the skeleton is composed of keratose, that 

 is, of horny matter, as in the sponge of commerce, the group is 

 known as the Keratosa. If the skeleton consists of lime, the 

 group is known as the Calcarea, or Calcispongia ; and if the skel- 

 eton is made of silica, the group is called Silicea. To the last 

 group belongs the fresh-water sponge, in which the skeleton is 

 made up of very fine spicules of silica. Knowing this fact, the 

 amateur needs not to be deceived by the green aspect of his 

 specimen, when it is found fresh and occupying its native habi- 

 tat ; for, instead of the simple gelatinous feel of the conferva, 

 our little Spongilla, when taken between the fingers, imparts a 

 crinkly feeling due to the presence of these spicules of silica. 



The sponge was long regarded a vegetable ; and in Japan, I 

 am told, the term for sponge literally means "sea-cotton." Bi- 

 ologists to-day agree in assigning the Spongida to the animal 

 kingdom. Indeed, if one of the flagellate cells, or " separate sar- 

 coids," with some protoplasm adhering, be carefully detached 

 from a colony, it will move about with its vibrating cilium, and, 

 like an Amoeba, will project the adhering protoplasm into many 

 pseudopodia, or false locomotive organs, of never ceasing change 

 as to form and number. 



When first studied abroad, the fresh-water sponge was put into 

 a genus, Spongilla^ containing two species, 6". lacustris, and S. 

 fluviatilis. Afterwards the genus Meyenia was erected, into 

 which S. fluviatilis was placed ; and, later, the other species be- 

 came known as S. lacustroides. It is an interesting fact, that 

 these two European species have American representatives. 



The specimen of Hetero7iieyenia ^j'^/^r/ mounted by Mr. Devoe, 

 will prove highly interesting, if attention be directed to the fol- 

 lowing objects, easily observed upon the slide. 



I. The skeleton spicules. These are of pure silica, and very 

 translucent, but do not polarize well. They are slightly arcuate, 

 or bow-shaped, in form, and are exquisitely sharp at both ends. 

 Indeed, in respect of sharpness, no cambric needle is compar- 

 able with them. Shown under high powers, these tiny bows are 

 not uniformly smooth, but are occasionally studded with very 

 minute spurs. 



The economy of this studding of the spicules with these point- 

 ed spurs is, I think, plain, and is really beautiful. They help 



