August 1, 1S60.J 



SCIENCE. GOSSIP. 



1S1 



specimens of red algas of various species, and on 

 looking at these on the day named, 1 found them all 

 nicely growing, having the delicate, plump, trans- 

 parent pinky -red colour, which is characteristic of 

 them when in the sea, under the most favourable 

 circumstances, while plants of the same species 

 which at the same time I carefully deposited in 

 the tanks, have become so entirely grown over with 

 conferva?, that their character is lost. In Hard- 

 wicke's Science Gossip for May, 1865, p. 117, I 

 recorded how once, by accident, I succeeded in 

 growing Delesseria sanguinea in a deep and almost 

 quite dark hole in a tank. 



The shells of Murex from Weymouth not only 

 thus ahound with algse, as described, but arc 

 frequently met with rich in numerous parasitic 

 animals — as Serpulce and Sabella of several species, 

 Sabellaria, Spio, and other things. The shells of 

 living Nassa reticulata (Dog Whelk), found in the 

 Baltic Sea, are usually covered with colonies of a 

 little zoophyte— Coryne; but I have not seen English 

 specimens of Nassa thus infested. The shells of 

 Buccinum, Purpura, Natica, and Fusus, when in- 

 habited by their proper molluscs, are never grown 

 over with any animal parasites, as far as I have had 

 opportunities of seeing them ; but when the same 

 shells are occupied by hermit crabs (Pagurus), they 

 — the shells — are then often densely covered with 

 colonies of another beautiful little zoophyte 

 (Hydractinia echinata), except at that part of the 

 shell which is dragged along the ground by the crab, 

 and this portion is not only free from zoophytes, 

 but is polished with the friction. 



Last Sunday I had brought me a half-grown 

 female living specimen of the edible crab (Cancer 

 pagurus), the carapace measuring 10 c. 2 m. long, 

 and 16 c. 4 m. broad. On this carapace has 

 grown, and is still there, a living oyster (Ostrea 

 edulis) measuring 8 c. 3 m. x 7 c. 7 m. This oyster 

 is between four and five years old, the age of the 

 mollusc being well known by its appearance, as it is 

 a cultivated article of commerce, and a fixture 

 during its life. Consequently the crab cannot have 

 changed its shell during the existence of the oyster 

 upon it, a period of from four to five years. But 

 when younger, this crustacean (C. pagurus) exuviates 

 much oftener. Thus, in our aquarium, on the 2nd 

 of March, 1864, a small specimen, measuring 3 c. 

 3 m. x 2 c. 1 m., cast its shell, and when it appeared 

 in its new coat it was 4 c. 4 m. x 2 c. 7 m. On 

 Eebruary 2Sth, 1865, it again exuviated, and ap- 

 peared with a carapace of 6 c. 9 m. x 4 c. 5 m. On 

 April 14th, 1866, it once more changed its shell, 

 and now the crab, which is still in the aquarium 

 and doing well, is quite a portly fellow of 9 c. 8 m. 

 x 6 c. m. These figures do not present to the 

 imagination what the empty shell and the newly 

 coated animal convey to the eye when the two are 

 placed side by side, and unless one has seen the 



operation as I have often done, it is difficult to 

 believe that the comparatively large creature has 

 emerged from the small case, especially after the 

 lapse of a day or two, when the newly clothed 

 creature has had time to get hard, and can be felt 

 with the fingers to be so. 



This article is already too long : if it were not so, 

 I would describe the manner in which I have seen 

 various crustaceans get out of their old shell, and 

 what they do before and after the change. But this 

 I must reserve for another time. 



W. Alford Lloyd. 

 Zoological Gardens, Hamburg. 



THE GREAT SAW-ELY (Urocerus gigas). 



rpHE other day I saw, for the first time, this fine 

 -*- insect alive. My daughter called my attention 

 to it on a new larch telegraph-post near Ditton, Cam- 

 bridge. Having secured the captive, we came to the 

 conclusion that it had as good a right to its life as 

 ourselves, and put it back on the bark, where, after a 

 few flights, it settled again, and began trying all the 

 bare places on the bark for one to deposit its eggs. 

 Hunching up its great body so as to bring the point 

 of the sheath to the desired spot, it in vain tried to 

 set its auger-like ovipositor to work. Again and 

 agaiu it failed, still trying as busily as ever, and then, 

 finding that our lady friend could make no hand at 

 it, I examined the instrument, and found it had 

 grown to only half its proper length in this 

 specimen. 



Fig. 167. The Great Saw-fly (Urncerus gigas). 



The black ovipositor in a perfect insect (we found 

 a smaller one busily at work lower down the post) 

 readies to the extremity of the sheath ; and the 

 instinct of the creature induces it to bend the body 

 so that the point of the sheath and the ovipositor 

 together may make the first impression at the desired 

 spot. The animal must have some means of judging 



