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INVERTEBRATE ZOOLOGY 



The Gonophore and Its Reduction. — An individual among the 

 coelenterates which bears the gonads is termed a gonophore. 

 Ordinarily, this is a free-living medusoid individual (Fig. 52 A) 

 with gonads either on the manubrium or on the radial canals of 

 the gastrovascular system. In some representatives of the class 

 Hydrozoa, the medusoid generation is lacking. This condition 

 is usually the result of a process which is designated as gonophore 

 reduction. Usually, the gonophores have their origin as products 

 of asexual reproduction from the hydroid individuals. Under 

 ordinary circumstances, they undergo development to a certain 

 stage while still attached to the hydroid and are then liberated. 



Fig. 52. — Gonophore reduction. A, free gonophore, an independent medusa; 

 B, a naedusa which remains permanently attached to hydroid colony and fails 

 to develop either tentacles or mouth; C, still further reduction of gonophore to a 

 simple manubrium (the spadix) surrounded by gonads; D, gonads produced 

 around a slight entodermal rudiment of the manubrium as in Hydra. {After 

 Kingsley) . 



In some instances, however, freedom is never gained, then the 

 gonophores remain permanently attached to the parent hydroid 

 (Fig. 52 B-D) and organs essential to the independent existence 

 of the gonophore fail to develop to a functional stage or degen- 

 erate entirely. By the selection of different examples, a finely 

 graded series of steps in the degeneration of the medusoid may 

 be secured. A greatly reduced gonophore comprises little more 

 than an ectodermal bag within which the germ cells are arranged 

 about a core of entoderm called the spadix. The spadix repre- 

 sents the remains of a degenerated manubrium. The term 

 sporosac is applied to such a reduced gonophore (Fig. 52 C) 

 attached to the body of a hydroid individual. In some species 

 of Corymorpha, medusae-bearing gonads are formed. Though 

 the medusae pulsate in futile fashion for several days, they never 

 break away from the parent polyp. The ultimate in gonophore 



