ZOOLOGY. 529 



within each other as in the preceding animals, but behind 

 each other, so that the present circle consists of multiplied 

 Cystic animals. 



3230. The Annulate animals must represent the 

 developmental stages of the tegument, while the viscera 

 make a retrograde step Tactile animals. 



3231. The tegument has two functions: it is an 

 organ of respiration and of general feeling or sensation. 

 In both cases it passes through three stages of develop- 

 ment. 



It is either entirely a branchia, i. e. reticular in cha- 

 racter ; or the branchiae become individualized in certain 

 situations and partly horny, constituting branchia proper ; 

 or finally, the tegument is converted into an air-breathing 

 organ, trachea or air-tubes. 



3232. It either feels with its whole surface, or by 

 papilla; or the branchiae change into horny feet; or 

 lastly, into alary appendages or wings. The Ancyliozoa 

 consequently divide into Reticular or Papillary animals ; 

 into Branchial or Pedal, and into Tracheal or Winged 

 animals. 



3233. As the arterial character preponderates in these 

 animals, so do the venous organs, especially the liver 

 and renal structures, retrograde. 



3234. The body is now an intestinal and tegumental 

 body with predominating respiratory and sentient organs ; 

 here therefore sensitive papillae, antennae, feet and wings, 

 appear in abundance. 



3235. With the retrogression of the viscera, the 

 glandular structure also and large proportional bulk of 

 the sexual parts disappears. They assume the form of 

 the intestine and tegument, i. e. become tubes. 



The spawn like the milt consists, as a general rule, 

 of only two long membranous tubes, running near the 

 intestine. 



3236. The external sexual parts belong to the sense 

 of feeling and follow the developments of the tegument ; 

 they make their appearance as antennae, and are usually 

 accompanied by foot-like accessory organs. 



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