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If we open one of the large -white lumps (Phallusia ma- 

 millata) lengthwise, we see that the coarse external cartilagi- 

 nous coat or mantle contains a second much more delicate sack, 

 connected with the first in two places corresponding with the 

 visible external openings. The external coat is principally formed 

 of a substance very similar to the so-called cellulose, the mem- 

 branous matter of vegetable cells and once believed to be it. 

 The inner sack opens from the orifice at the end into a large 

 cavity containing the gills, the sides of which are coated with 

 a ciliated sort of trelliswork. At the bottom of this cavity is 

 the true mouth, into which small particles of nourishment are 

 conducted together with the water, by means of the action of 

 the fringes of the gills. The intestines, which are wound into 

 a kind of ball, lie, together with the organs of circulation and 

 generation, at the bottom of the inner sack, and the excretions 

 are emptied through the lateral opening in the body, which 

 also serves as a duct for the products of generation and for 

 the ejection of water from which the air is exhausted. A nerve- 

 ganglion, with radiating nerve-fibres, lies near the orifice into 

 which the fresh water is received. 



The Ascidians , a group of the Sea-squirts, are almost all 

 adhesive animals, and either remain single , like the above- 

 mentioned Phallusiae, which are generally the largest species, 

 or they form colonies in which the individuals are connected 

 by roots (social Ascidians, for instance Clavellina). The com- 

 posite Ascidians form a third group. These animals are imbed- 

 ded in a common sack and arranged in a certain manner. To 

 this group belong the rind-like crusts seen on the rocks of 

 the tank, in which one can distinguish with the naked eye the 

 pretty little round animals, like rosettes , gathered round a 

 common excretory vent. Till now only one kind of unattached 

 swimming Ascidian is known, the Pyrosoma, a hollow gela- 

 tinous tube, shaped like a fir-cone , upon which the single 

 animals stand up like the little pegs on the barrel of a musi- 

 cal box. They belong to the pelagic animals which cause the beau- 

 tiful phosphorescence so often observed in the sea. This creature 

 is very seldom found in the Aquarium , for it is one of the 

 rarest and least unterstood animals in the Gulf. 



A discovery made by the Russian zoologist Kowalewsky has 

 connected the history of the generation of the Ascidians with 

 that of the origin of the vertebrate animals. That naturalist 

 observed th'at from the eggs of the ascidians were developed 

 unattached swimming larvae provided with a moveable oar-tail 



