342 M. Weltner on the Survival of Spongillge. 



to keep perennial freshwater sponges from the autumn to the 

 middle of the summer I ascribe chiefly to want of nourish- 

 ment. We know almost nothing of the food of the Sponyillce. 



On the 16th October of last year I again obtained six lai'ge 

 s[)ecimens of Ephydatia Jiuviatilis from the Tegelsee. The 

 smallest of these sponges measured 5^ centim. in length, the 

 largest 10 centim. ; the thickness of these crusts was 2| 

 raillim. in the smallest and nearly 5 millim. in the largest 

 specimen. All the six were examined for ova, segmentation- 

 stages, and larva in the most different parts of their bodies 

 (at this season there is no longer any semen). Four were 

 neuters, and will be no further referred to. The two others 

 were female, and, as I expressly note, completely filled with 

 segmentation-stages and larvae. These two specimens were 

 placed in large aquaria containing 3-4 litres of water *, into 

 which I had previously put sand and Elodew. The glass 

 vessels were disturbed as little as possible and stood in an 

 unwarmed room of the Zoological Museum. During the 

 whole time the water was only once changed, and this quite 

 at the commencement. From these two sponges larvae 

 swarmed uninterruptedly from the 16th October onwards; 

 the last free-swimming larvte were observed on the 30th 

 October. One of these Spongillce constantly showed three 

 large excurrent tubes and began in December gradually to 

 diminish in volume ; the derm and oscula first disappeared 

 and the points of the spicules projected freely. On the 2nd 

 January the temperature of the water in this vessel, which 

 stood close to the window, had fallen below 32° F., and when 

 the vessel was turned for observation the water all at once 

 became solidified in large leaves down to the sponge, which 

 was in the middle. Both aquaria were then brought into a 

 place situated between two warmed chambers. The sponge 

 just described did not, however, recover; it is now much 

 reduced, nearly the whole skeleton lies bare, in two places 

 the derm stands off in the form of large closed bladders, and 

 in the upper part of the sponge there is only a minute 

 osculum. 



The other of the two larva-bearing Spongillce constantly 

 changed the number and position of its oscular tubes during 

 the first month of its residence in the aquarium ; from the 

 16th November onwards, when a passing frost occurred^ it 

 showed only a few oscula, and from the 10th December the 

 number and position of the two excurrent tubes remained 



* The water was derived from the local water-supply, which receives 

 its Avater from the Tegelsee. 



