178 BRITISH TYROGLYPHID^], 



stainable layer containing scattered nuclei; tlien the 

 testes enlarge greatly, and their posterior poles become 

 almost arched over by the pileus-like germinal portions. 



In the female, immediately after the second (first 

 nymphal) ecdysis, a vigorous growth of the hypo- 

 dermal tissue occurs at the posterior end of the anal 

 slit. Later on the hypodermis invaginates at this point 

 and forms a thick-walled, clavate sack between the 

 rectum and the ventral surface. It is easy to under- 

 stand that the receptaculum seminis is formed from this 

 invagination ; the opening, during the whole second 

 nymphal stage, lies close behind the anal slit. 



Turning to the ovaries and their ducts we see that 

 the cell-mass at the junction of the ducts has greatly 

 increased and assumed an almond shape ; soon a 

 longitudinal split appears which gradually widens; 

 finally the median cell-mass forms a hollow three- 

 sided pyramid at the dorsal angle of which the two 

 oviducts enter by a common opening. It is easy to see 

 that the cell-mass from which the accessory glands and 

 the penis of the male are formed becomes the vagina 

 in the female. 



The oviducts have greatly increased in length, and 

 make a sharp turn outward ; they have not as yet any 

 lumen, this appears shortly before the ecdysis. 



The ovaries still retain their globular form, but have 

 moved somewhat backward at the side of the rectum. 

 A change in the cells occurs in the ovaries as it does in 

 the testes ; it is different from that of the male organs, 

 but equally results in the formation of a germ-layer. 

 Until the second ecdysis the germ-gland consists of 

 small indifferent cells, but after it a difference arises 

 between the peripheral and the central cells ; the first 

 assume an epithelial character, they increase to many 

 times their former size, but retain their distinct outline. 

 The central cells grow but little, but gradually lose 

 their outlines ; the protoplasm becomes a homogeneous 

 layer, in which nuclei are embedded; later on even 

 these break up into finely granular, refractive pieces, 



