SOME NEW BOOKS. 



The Monograph on Salpa. 



The Genus Salpa. A Monograph, with 57 plates. By W. K. Brooks, Ph.D., 

 LL.D., Professor in the Johns Hopkins University. Memoirs of the Biologica 

 Laboratory of the Johns Hopkins University, II. Baltimore: The Johns 

 Hopkins Press, 1893. 



Salpa is itself so interesting an animal and belongs to so interesting 

 a group that the results of Professor Brooks's researches deserve at 

 once a fuller and a less technical account than is given usually in a 

 review. The account need not be technical, for all morphologists 

 who take a special interest in the Tunicates will have to pore over this 

 magnificent memoir. Even to those who pay no special attention to 

 them, the Tunicates are interesting because they seem to possess, more 

 certainly than any other group, indications that they represent the 

 stock from which the vertebrate animals were derived. But in addition 

 to this general interest. Dr. Brooks has brought before us matter so 

 surprising that it may well attract the notice of all who care for the 

 problems of nature. 



Fig. 1.— Salpa pinnata: a specimen of the aggregated form seen from the left side. 



Salpa is a transparent swimming Tunicate, which may be compared 

 to a barrel, open at both ends. It is, in fact, an enormous Pharynx 

 which swims through the water, gulping great mouthfuls at every 

 contraction of its muscles. A rod-like gill stretches from above the 

 wide open mouth in front, through the hollow of the barrel, to below 

 the posterior aperture behind ; but this is so narrow that it offers no 

 obstruction to the flow of water through the animal. Along the ventral 

 line of the inside of the barrel runs a ciliated, mucus-secreting band, 

 which is the homologue of the endostyle in ascidians and Amphioxus. 

 A.t the posterior end of the barrel, in a thick mass, are contained the 

 viscera, and this mass is the only part of the animal which is not 

 transparent. Representing the hoops of the barrel are a number of 

 muscular bands by the contraction of which the water is driven through 



