384 K. T. GUNTIIER. 



cavity and its ducts into excretory and gonad-bearing portions 

 we arrive at the condition typical of the higher types of 

 MoUnsca in which a second pair of ducts is developed in con- 

 nection with the discharge of the genital products. Such is 

 the condition in the Cephalopoda iu which the gonadial peri- 

 cardial cavity remains undivided, but in the Polyplacophora 

 the gonadial coelom has become completely separated from 

 the renal coelom. In the Chtctognatlia the gonadial ccelomic 

 spaces have become separated for the purpose of dividing 

 the male and female sexual cells (text-fig. 10). 



Both Cha3tognatha and MoUusca are hermaphrodite. The 

 parent germ-cells originate at the same time, and are indis- 

 tinguishable. It might be suggested that the determining 

 factors of sex only come into operation after the germ-cells 

 have migrated into separate cavities in which different nutri- 

 tive conditions prevail. 



Conclusions. 



The very numerous and close resemblances Avhicli exist 

 between the Chajtognatha and every class of Mollusca show 

 that there is no single structure, or absence of structure, of 

 importance iu the Cheetognath anatomy which is not capable 

 of being developed somewhere within the limits of the 

 Molluscan phylum, and that many apparently insignifi- 

 cant features have their exact counterparts therein. In 

 short, granted similar conditions of life, a Chastognath type 

 might be expected to arise from the Molluscan stock. On 

 the other hand, the claims which have been put forward in 

 favour of the alliance of the Chtetognatha with tlie Annelida 

 or Nematoda are not capable of being supported by so 

 extensive or consistent an argument. 



Can the Cha3tognatha be definitely associated with any 

 one class of Mollusca, or are their relationships more 

 general ? 



The following morphological characters are among those 

 obviously of importance : 



