DEVELOPMENT AND IMMATURE STAGES. 175 



At the first ecdysis the generative glands separate 

 from the anal opening, and move somewhat forward ; 

 at the points where they had been attached to the anus 

 the cells multiply rapidly, and give origin to short, 

 solid, cellular cylinders, from which the ducts are 

 formed; the commencements of the right and left gene- 

 rative glands join, and appear as if united by a bridge. 



At the point of junction of the two future ducts the 

 outer nascent genital organ of the nymph is formed 

 from the hypodermal tissue ; it consists of the two 

 sucker-pockets, each containing one sucker. The 

 pockets are formed by invaginations of the hypodermis. 

 The suckers originate at the end of the newly-formed 

 retractor muscles, which receive a dome-like coating 

 from the hypodermis. 



The further development of the sexual organs during 

 the first nymphal stage is almost confined to the 

 increase in size of the generative gland and ducts ; the 

 latter especially lengthen greatly. This involves an 

 alteration in the position of the gland ; which, however, 

 occurs differently in the two sexes, and even thus early 

 indicates the sexual nature of the creature. In the 

 adult male the vasa deferentia run directly from the 

 testes to the genital opening. We must therefore 

 look upon those nymphs where the duct proceeds 

 directly backward as males ; in them the testes arrive 

 thus early at their final position on each side of the 

 rectum. In the female the growing oviduct makes a 

 strong bend to the side, by which the ovaries are 

 pushed laterally ; they only shift to the side of the 

 rectum after the formation of the loop. The ducts of 

 the generative glands are still solid cylinders ; in 

 transverse sections of them the radial arrangement of 

 the cells may be seen. Above each sucker-pocket a 

 comb-like cellular growth appears; from which, at a 

 later stage, the accessory glands of the male and the 

 vagina of the female develop. At the end of the first 

 nymphal stage the testes have assumed an oval form ; 

 their long diameter is about "018 mm. The ovaries 



