684 



INVEBTEBHATE MORPHOLOOT. 



spots probably representing eyes, and the subneural 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 



ma 



Fig. 290. — A, Salpa mueronata, the sbxtjai Fobm, and B, Salpa democra- 

 tica, THB Non-Sexual Form of Salpa democratica-mucronata (after Glaus). 



6, cl = cloaca. m = brauchial pore (mouth). 



cp = ciliated pit. ma = test. 



em = embryo. n = nerve-ganglion. 



en = endostyle. nu = nucleus. 



7t = 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 (B) 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 iust 



