G. GENERAL NATURAL HISTORY AND ZOOLOGY. 339 



niembered, exists solitary and in chains. He concludes that 

 the solitary Salpa is the female, and produces a chain of males 

 by budding, and discharges a single egg into the body of 

 each one of these before birth. These eggs are impregnated 

 while the chain-salpse are very small and sexually immature, 

 and develop into females which give rise to males by bud- 

 ding. After the fcetus has been discharged from the body of 

 the male, the latter attains its full size, becomes sexually ma- 

 ture, and discharges its spermatic fluid into the water to gain 

 access to the eggs carried by other immature chains. It is 

 worthy of notice that although Chamisso's announcement of 

 the occurrence of alternation of generations among animals is 

 thus seen to have been drawn from the study of animals which 

 do not present an instance of it, this mistake has been of the 

 greatest usefulness, since it has led to our knowledge of the 

 numerous instances of true alternation which now form such 

 a large and important chapter of zoological science. 



The relation in which Salpa stands to the other tunicates 

 shows also that no abrupt line can be drawn between alter- 

 nation and ordinary sexual reproduction, but that they are 

 different forms of the same process. On another occasion he 

 attempts to show how all the strange peculiarities of Salpa 

 receive a simple explanation upon the theory that Salpa is 

 the descendant of an ordinary tunicate which has been mod- 

 ified by natural selection. Amer. JVaturaUst^ November. 



STEPHANOCEROS ON SUBMERGED PLANTS. 



Dr. Pierce has observed the rotifer known as the Stephano- 

 ceros growing on submerged plants near the Schuylkill River. 

 It had not been previously noticed in that region. Dr. Pierce 

 found that it fed on paramecia, which it seized by the ex- 

 tremities of its horns, and passed to its mouth by movements 

 of the cilia which clothe them from apex to base. This Ste- 

 phanoceros is inclosed for much of its length in an inflexible 

 sheath ; but at stated intervals the projected portion sepa- 

 rates from its sheath, and swimming to another locality lo- 

 cates itself by the base. This Dr. Pierce observed to take 

 place several times. He never saw any foecal discharges from 

 the animal, and suggests that the solid case is formed from 

 them, and that the migration of the Stephanoceros is due to 

 the final obstruction of this means of deposit. 



