502 



BULLETIN OF THE 



although the solitary. individuals, and those which have been set free 

 by the breaking up of a chain, move by jerks. Since the blood circu- 

 lates in the sinus system which surrounds the branchial sac and atrium, 

 and also penetrates the cavity of the gill, which is simply part of the 

 body cavity shut off by the union of the branchial and atrial tunics, 

 its aeration is amply provided for. 



If a little carmine is added to water containing Salpse, the manner 

 in which the food is conveyed to the mouth can be distinctly seen. The 

 carmine, drawn in with the water, adheres to the inner surface of the 

 branchial sac, anterior to the epipharyngeal ridges, and is then rolled 

 along by the cilia until it reaches these ridges, the cilia of which are 

 so set that they change its direction and convey it to the anterior end 

 of the endostyle, the cilia of which gradually carry it backward to- 

 ward the mouth. The contraction of the muscles now becomes more 

 vigorous, and at each contraction the body is so compressed that the 

 epipharyngeal ridges come into contact with the haemal or branchial 

 surface of the gill, and the water is forced along the tube thus formed, 

 driving the food before it to the mouth. 



Digestive organs of very young solitary Salpa, figured with the neural side below : b, outer 

 tunic ; d, wall of atrium ; g, atrial aperture ; h, cavity of branchial sac ; i, cavity of atrium ; I, 

 epipharyngeal ridge; m, endostyle ; n, gill ; o, mouth ; o', oesophagus; o", stomach ; </", 

 intestine ; o"", aims. 



The Digestive Organs. — In the adult these are so obscured by the 

 organs which overlie them that it is almost impossible to trace their 

 course, which must therefore be studied in the young. Fig. 4 shows 

 the atrial and part of the branchial chamber, and the digestive organs 

 of a very young solitary Salpa, in which the cavity of the intestine is 



