Gonad synonyms

The gonads are on the radial canals or on the stomach (Ptychogastridae), and each gonad may be divided into two by a longitudinal sub-umbral muscle-tract.

In the female the gonad is complex as in flatworms, composed of a germary for the formation of the eggs, and a vitellary, much more conspicuous and alone figured (ov), consisting of a definite number of large nucleated cells for the nourishment of the eggs.

In these and other Chaetopods the coelom is also put into indirect relations with the outside world by the nephridia and by the gonad ducts.

It seems that the posterior nephridia are mainly gonad ducts, and the gonads are developed in close association with the funnels.

On this view then the Aplacophora are more primitive than the Polyplacophora in the relations of coelom, gonad and coelomoducts; and the genital ducts of the Chitons have arisen either by metameric repetition within the group, or by the gradual loss of an original connexion between the generative sac and the renal tube, as in Lamellibranchs and Gastropods, the generative sac acquiring a separate duct and opening to the exterior on each side.