634 



INVERTEBRATE MORPHOLOGY. 



spots probably representing eyes, and the subueural gland is 

 present as usual. 



Each species of Salpa, however, presents two distinct 

 forms (A and B\ differing in shape and in the number of the 

 muscle-bands which are found in the mantle and having like- 

 wise a different origin. In the sexual form (A) reproductive 

 organs are developed, the ovary usually containing but a 



em 



cl 



nu 



h A 



ma 



FIG. 290. A, Salpa mucronata, THE SEXUAL FORM, AND B, Salpa democra- 



lica, THE NON-SEXUAL FORM OF Salpa democratica-mucronata (after CLAUS). 



c, cl = cloaca, in = branchial pore (mouth). 



cp ciliated pit. ma = test. 



em = embryo. n = nerve-ganglion. 



en = endostyle. nu = nucleus. 



U heart. si stolon. 



single ovum. This when fertilized (em) is passed into the 

 atrial cavity, the follicle-cells with which it is surrounded 

 forming an adhesion to the wall of the cavity, and later 

 modifying to form a structure recalling the placenta of the 

 Mammalian Vertebrates by which nourishment is conveyed 

 from the parent to the embryo. As the result of the develop- 

 ment of this ovum the non-sexual form (.#) is produced, which 

 is characterized not only by its general form, but also by the 

 possession of a stolon (st) arising from the branchial sac just 



