300 Dr. A. WierzejskI on FresTiwater Sponges. 



contractile substance. They originate from nucleated paren- 

 chyma-cells by the development of a gig-antic vacuole, the 

 walls of which are chemically differentiated. 



Their behaviour with different reagents is worthy of notice. 

 A moderately strong solution of acetic acid, after acting for a 

 short time, causes them to burst, when the contents imper- 

 ceptibly disappear, and only the nuclear vesicle with traces 

 of the excessively fine membrane remains. An interrupted 

 galvanic current produces the same phenomenon. Ammo- 

 nia added by drops under the covering-glass effects a remark- 

 able alteration. A double vesicle is produced ; the inner one 

 occupies an excentric position, its walls show a folding, its 

 contents remain hyaline. The same alteration of the vesi- 

 cular cells is observed during the gradual decay of the sponge. 

 Solutions of hyperosmic acid (1 per cent.) and nitrate of 

 silver produce no perceptible change ; but if the preparations 

 are exposed to the light the vesicular cells treated with the 

 former solution acquire a light brownish colour, those with 

 the second remain limpid, and only the granules and swellings 

 of the contractile substance adiiering to the surface are black- 

 ened. By treatment with strong alcohol and 1 per cent, 

 solution of chromic acid the alteration is most striking. As 

 a rule double vesicles are produced ; the inner presents very 

 multifarious images ; its contents appear sometimes finely 

 granular, sometimes reticular, sometimes nodular, &c. Fine 

 filaments are often seen stretched from the surface of the inner 

 vesicle to the inner surface of the outer one. As a matter of 

 course the great variation of the images corresponds to the 

 different degrees of concentration of the solutions employed, 

 also chiefly to the different stages of develo])ment of the 

 vesicular cells and their varying chemical constitution. 



The vesicular cells treated with alcohol and chromic acid 

 very readily imbibe picrocarmine, and thus strike one at once 

 in preparations. On the contrary, they prove very resis- 

 tant to aqueous solutions of aniline colours. 



Their behaviour towards Lugol's solution is also very cha- 

 racteristic. Thus, if examples taken from dried specimens 

 are placed in water for a few minutes and then treated with 

 this solution, the shrivelled vesicular cells immediately acquire 

 a light chestnut-brown colour, while the other elements 

 become yellowish. After the partial volatilization of the 

 iodine the colour changes to violet or wine-red. If a stronger 

 solution be employed a dark brown colour is obtained. Pre- 

 cisely similar results are obtained by treating alcoholic prepa- 

 rations with Lugol's solution, only the action is not so rapid, 

 and the specimens must be allowed to lie longer in the water. 



