508 BIOLOGY. 



intestine only the vascular system, they are still governed 

 by the water, and live therefore for the greatest part in 

 this element. They have the first mode of respiration 

 and thus an aqueo-respiratory process possess branchiae 

 but not tracheal tubes. 



3126. The sexual parts, which in the Germ-animals 

 were still coalesced for the most part with the body, here 

 become self-substantial through the separation of the 

 teguments, make their appearance as a repetition of the 

 digestive system under the condition of a free or sepa- 

 rate system, and are evolved into true ovaria and even 

 male parts Sexual, Glandular animals. 



3127. The first step towards the evolution of male 

 parts is, however, only half achieved. Only one testis 

 originates, while the other remains behind as ovarium 

 Androgynous or Bisexual animals. 



3128. These animals, which are characterized by the 

 vascular system, and by the first self-substantial or exter- 

 nal sexual parts, which indicate organs of sense, are the 

 Conchozoa, such as the Mussels, Snails, and Kracken. 



* 



Circle III. Respiratory Animals. 



3129. When once the intestinal and vascular system, 

 through perfection of their individual parts, such as the 

 liver and branchia, and through separation of the sexual 

 parts, are completed ; then the individualization of the 

 tegument steps into view, and it becomes an independent 

 respiratory system. 



3130. Through the increased process of oxydation the 

 tegument hardens and is converted into horn. All 

 induration, however, only takes place in opposition to 

 soft places. The tegument therefore separates into hard 

 and soft rings Annulate animals. 



3131. The annulate tegument is a tracheal tube 

 wholly converted into a body. To distinguish it from the 

 general tegument it may be called the cutis or skin Cuta- 

 neous animals. The annular tegument may be regarded 

 as a series of cysts placed one behind the other. The 



