VERTEBEATA. 109 



is reduced to a median band. The viscera are compressed together 

 at the end of the ventral side and form the so-called nucleus. 

 Solitary generations which reproduce themselves by means of stolons 

 regularly alternate with sexual animals which are budded from the 

 stolon and united in chains. The maturity of the female sexual 

 organs precedes that of the male organs. The single egg develops into 

 an embryo which is nourished within the brood-pouch of the viviparous 

 mother by means of a placenta, and becomes a solitary Salpa (asexual 

 form) (fig. 567 c). 



Fam. Salpidae. Salpa Forsk., S. pinnata Forsk., S. democratica Forsk., 

 8. mucronata Forsk. (chain form), Adriatic and Mediterranean. S. africana 

 Forsk., S. maxima Forsk. (chain form), Adriatic and Mediterranean. S. 

 chordiformis Quoy. Gaim., S. zonaria Pall, (chain form). 



Order 2. CYCLOMYARIA, 



Body cask-shaped, mouth and atrial opening surrounded by lobes, 

 with delicate mantle (fig. 568). The muscles are in the form of 

 closed rings. The dorsal wall of the pharyngeal cavity is formed by 

 a branchial lamella which is pierced by numerous slits, is placed 

 obliquely or is bent and stretched far forwards (D. denticulatum). 

 The digestive canal is not compressed into a nucleus. The ovaries 

 contain several eggs. The testes attain maturity simultaneously 

 with the ovaries. In the first asexual generation there is a large 

 auditory vesicle on the left side. The development takes place by 

 means of a complicated alternation of generations. 



Fam. Doliolidae. D. denticulatum Quoy, Gaim., the gill is bent and is 

 pierced by about forty-five slits. D. Mulleri Krohn. The' gill is straight, with 

 ten to twelve slits on either side, Mediterranean. 



CHAPTER IV. 



VERTEBRATA.* 



Bilaterally symmetrical animals with an internal skeleton (vertebral 

 column), of which dorsal processes (upper vertebral arches) enclose the 

 nervous centres (brain and spinal cord), and ventral processes (ribs) 

 the cavity in which the vegetative organs are enclosed. There are at 

 most two pairs of limbs. 



The various animals included in this group were first put together 



* Besides the works of Cuvier, F. Meckel and J. Miiller, compare K. Owen 

 " On the anatomy of Vertebrates." Vol. I., II., III., London, 1866-68. 



C. Gegenbaur," Grundziige der vergleichenden Anatomie," 2 Aufl. Leipzig, 1878. 



Th. H. Huxley, " A Manual of the Anatomy of vertebrated animals. 11 London, 

 1871. 



