176 BRITISH TYROGLYPHIDvE. 



maintain their original round form, and are about 

 02 mm. in diameter. 



In the first nymphal ecdysis, as in the larval, the 

 sucker-pockets are formed, but each contains two 

 suckers; they lie between the epimera of the fourth 

 pair of legs, and are only slightly directed upward. 

 Kramer speaks of an external opening ; this must not 

 be taken literally; the external opening only appears 

 at the last ecdysis. 



It is during the second nymphal period that the 

 development of the genital organs makes most pro- 

 gress ; the difference between the sexes becomes 

 evident, inasmuch as the characteristic accessory 

 organs are formed. Hitherto the progress of the male 

 organs has been almost parallel to that of the female, 

 but a sharp distinction between the two now commences, 

 and renders separate descriptions necessary. 



In the male the comb-like cell-mass which lies over 

 the median chitinous piece of the external genital 

 organs at the juncture of the vasa deferentia increases 

 continuously in size. At its anterior end two solid 

 cellular papillae bud out and lengthen rapidly ; the 

 right one is almost exactly in a line with the left vas 

 deferens, and the left one with the right vas deferens ; 

 so that the vasa deferentia appear to cross above the 

 outer sexual organs. At the same time a globular cell- 

 mass arises from the median mass at the junction of 

 the vasa deferentia. A growth of cell- tissue may now 

 be seen between the two vasa deferentia ; it forks, and 

 becomes two strings of cells; finally its base thickens, 

 and forms a horse-shoe from which the supporting 

 sclerites of the penis are formed. If the organs be now 

 compared with those of the adult there is not any diffi- 

 culty in identifying them. The semicircular gland is 

 formed from the anterior cellular papillas by the two in- 

 creasing in size, and uniting at their bases. A lumen is 

 now formed in the central cellular body which has hither- 

 to been solid. At first it is a narrow central canal, but 

 widens surprisingly from the pushing outward caused 



