ZOOLOGY. 497 



In the ovum the tegument and its contents are not as 

 yet separated. Both consist of a transparent mucous or 

 gelatinous mass, as is exemplified by the vitellus and 

 albumen ; such is the case also in the Infusoria, Polyps, 

 and Acalephae or Sea-nettles. 



In the sexual organs, however, both parts separate into 

 membranous capsules or cysts, and glandular contents, 

 as in the roe or ovary ; milt or testes ; kidneys, with 

 furthermore the oviduct, penis, and urinary bladder. 

 The latter are sentient membranes. Such is the case 

 in the Bivalve Mollusca, and Snails. 



In the next place the tegument becomes, for the first 

 time, a self-substantial organ of sensation by appearing 

 as an envelope of the body; the vesical form is then 

 repeated, and by this means the annular character origi- 

 nates as a series of cysts arranged one behind the other ; 

 it is thus a veritable skin, from which, finally, the mem- 

 bers sprout forth, as in Worms and Insects. 



The Dermatozoa will accordingly range in three stages. 



1. Blasto- or Oozoa. 



2. Sexual animals. 



3. Cutaneous 



An annulated tegument, cutis or true skin, appears for the 

 first time in the Worms, with here and there lateral fila- 

 ments and tentacula. True feet and antennae appear 

 in the Crustacea or Crabs. Lastly, feet and wings in 

 the Insecta or Flies. 



3086. The external sexual parts, especially the male, 

 first make their appearance, and that indeed with a very 

 striking amount of development, in the Snails, and in like 

 manner the body of the Bivalve Mollusca or Mussels has 

 become almost a complete mass of ova or roe. In the 

 Cuttle-fishes the first traces or rudiments of urinary 

 organs appear. The animals which belong to this group 

 are accordingly the Conchozoa or Shell-animals. 



3087. Animals, which are directly resolvable into 

 sexual fluids, or that represent parts of the ovum, are 

 the gelatinous Infusoria, Polyps, and Acalephae. Unto 

 this category belong the Protozoa or Mucus-animals. 



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