526 F. W. GAMBLE AND J. H. ASHWORTH. 



The cells covering these branches of the gonidial vessel give 

 rise to male genital cells ; and the younger stages in their 

 development are therefore found in close association with 

 the blood-vessels of the lobe. The male genital cells are at 

 first small, uniform in size, and have large, sometimes 

 vesicular nuclei. These soon undergo divisions resulting in 

 the formation of stages in the development of spermatozoa 

 similar to those which are found in the coelomic fluid of 

 other species (see Gamble and Ashworth, 1898, PL 5, 

 figs. 30 — 34) . As in the female, the superficial portion of 

 the genital strand is unaltered epithelium, which also forms 

 the outer membranous covering of the reniform lobe within 

 which the developing spermatozoa are contained. The 

 branches of the gonidial vessel divide freely among the 

 developing spermatozoa, so that every portion of the reni- 

 form lobe is well supplied with blood. The genital strand 

 and the reniform lobe (or lobes) together form the testes of 

 the worm. 



In other species the reproductive cells leave the small 

 gonad at a very early stage of their development, and com- 

 plete their development while in the coelomic fluid. In 

 A. ecaudata the reproductive organs are large, being 

 produced in one or more outgrowths covered by epithelium, 

 and well supplied with blood-vessels. The reproductive 

 cells retain their connection with the gonad for a much 

 longer period, and in fact are not discharged until they are 

 nearly ripe. Hence reproductive cells in an advanced stage 

 of development only are found in the coelomic fluid of this 

 species. 



When the ova have attained a diameter of about 16 to 20//, 

 they break through the coelomic epithelium of the gonad 

 and fall into the coelom (except in A. ecaudata, in which 

 they are retained until they are almost ripe). The nucleus 

 increases in size and becomes vesicular, its diameter being 

 about half that of the ovum. There is generally also a well- 

 marked germinal spot or nucleolus. Very small yolk granules 

 ai*e deposited in the protoplasm. They are most abundant 



