The Microscope. 51 



method of research may be given: (1) Osmic acid until the 

 sponge is dark brown; then wash and place in 33 per cent, 

 alcohol; then picrocarmine. (2) Absolute alcohol; wash; 

 alum-carmine. (3) Corrosive sublimate solution, 40 per cent.; 

 haema oxylin. The sections must be very thin. 



How a Hydroid Attaches Itself. — Dr. W. K. Brooks de- 

 scribes (Z. A. vii., p. 709, 1884) an interesting feature in the 

 development of Eutima. It forms a planula as usual, the pro- 

 cess of the origin of the endoderm (by delamination) being 

 readily seen in the living embryo. Then an invagination oc- 

 curs, which, were one unacquainted with the whole history, 

 would be interpreted as the formation of a gastrula; but in 

 reality this is but the formation of a cement gland which is to 

 secrete the substance by which the young hydroid is later to 

 attach itself to some submarine object. 



Those who are interested in the common fresh-water Hy- 

 dra will find some interesting facts regarding its method of 

 fixing itself, and the way in which it walks, in a paper by Ha- 

 mann in the Janaische Zeitschrift, some three years ago. This 

 author describes cells at the base of Hydra, which send out 

 pseudopodia very much like those of Amoeba, and by means 

 of these, just as an Amceba walks the hydroid is able to change 

 its position. 



A Case of Symbiosis. — One of the most peculiar of animals 

 is the worm (?) Phoronis. Its development is very remarka- 

 ble. At one stage it develops a larval form known as Actino- 

 trocha, and this changes into the adult by apparently turning 

 itself inside out. An Australian species of the genus, recently 

 described, lives in colonies, each individual forming a tube in 

 the soft sea bottom. These tubes are usually arranged around 

 a large sea-anemone, so that it also lives in a tube. This doubt- 

 less is of great advantage to the worms as the thread cells of 

 the anemone kill food for them. 



In Australia a peculiar insect has just been discovered. It 

 belongs to the same family as our familiar forms known as 

 spittle insects, but its peculiarity consists in the fact that the 

 larva constructs a case which is largely composed of carbonate 

 of lime, and which in shape resembles the cases of the worms 

 known as Serpulce. 



