136 



Selections. 



[No. 7, NEW SERIES. 



opening in the mantle into a large gill-bag, the whole inner sur- 

 face of which is covered by a lattice work of oblique meshes, each 

 mesh being furnished with cilise in constant motion. The eddy- 

 occasioned by these cilise draws the water through the outer open- 

 ing into the gills. Each mesh forms a slit through which the 

 M ater flows outwards, and it is then thrown out through the other 

 opening in the mantle. In the case of the Salpce on the contrary, 

 the gill-bag forms the greater part of the body, and the gills have 

 the appearance of crooked beams stretched out from above to be- 

 low and from end to end of the bag. The wall of the gill-bag is 

 completely smooth, but each beam is full of a great number of 

 vessels. The water is swallowed in at the fore-end, winds round 

 the gills, and is then expelled at the hinder end. 



The order of the Ascidise consists of extremely unsymmetrical 

 animals, the two openings in the mantle of which are generally 

 very near each other, and attach themselves in jelly-like lumps to 

 rocks and sea-weed ; it consists of four families : — 



1st. Ascidise composite; 

 2nd. Ascidise sociales. 

 3rd. Ascidise simplices. 



4th. The " Fire-COnes" {Pyrosomida) which form a kind of 

 link between the composite Ascidise and the following order. One 

 finds swimming in (quantities in the Southern seas, jelly-like 

 bodies, sometimes a foot long, which are rather of the shape of a 

 fir-cone, and show a large internal cavity which possesses a circu- 

 lar opening at the broad end. The cone swims slowly with chang- 

 ing contractions, by which it expresses the water from its inside. 

 By night it shines with a clear splendour like iron at a white heat. 

 The light begins at a small point and spreads trembling over the 

 surface of the cone till the whole is in a glow. When such a cone 

 is narrowly examined it is found to be the common mantle for a 

 number of animals much like the Ascidise ; they approach them 

 in the structure of their gill-bag and in their mode of propagation, 

 but their distinct eye on the large ganglion, their power of swim- 

 ming, their phosphorescent nucleus and the position of the open- 

 ings in the mantle proclaim their affinity with the Salpce. 



