STUDIES IN THE EXPERIMENTAL ANALYSIS OF SHX. 227 



another at a glance (see figs. 1, 2, 3 and 4, PI. VII, 'Naples 

 Monograph' and again ' Quart. Journ. Micr. Sci./ vol. 54, PI. 

 SO, figs. 10, 11, 13, 14). Now, when the infected males take on 

 the female external characters they have never been found to 

 assume the juvenile flattened form of abdomen which charac- 

 terises the young stages of both males and females, but they 

 invariably take on the hollow trough-like form characteristic 

 of the adult breeding female and of her alone (see the 

 numerous figures on the plates referred to above). That is 

 the first objection to the view that the alteration of the male 

 is merely towards a juvenile condition, and anyone who will 

 examine the series of specimens exhibited in the South 

 Kensingfton Museum or in the Oxford Museum, or those 

 deposited by me at the Zoological Station at Naples, will at 

 once perceive the entire morphological difference of the 

 abdomen in the young and adult female, and the identity of 

 the modified male abdomen with that of the adult female. 



Secondly, with regard to the abdominal appendages. It is 

 not a question of the mere presence or absence of a few hairs, 

 as Professor Morgan has unfortunately been led to suppose. 

 The abdominal appendages of the juvenile and adult indi- 

 viduals differ as radically, if not more radically from oiie 

 another, than the form of the abdomen. In the young form 

 uf the female these appendages are short, stout and rod-like, 

 and provided with a very few short bristles, as shown in PI. 

 14, fig. 7 of this paper. In very young males similar 

 appendages are present, but they are lost at a very early 

 stage indeed, only the two anterior appendages being kept as 

 the copulatory styles. The form of these two appendages in 

 the young male is shown in PI. 14, figs. 1 and 2. 



The adult female, at the same moult at which it acquires 

 the characteristic adult form of abdomen, assumes a totally 

 different kind of appendage of the form shown in PI. 14, fig. 

 4. Here it is seen that instead of being stout and rod-like 

 with a few stiff hairs, as in the young females, the appendage 

 has become transformed into two wisp-like branches, the 

 exopodite being densely clothed with long plumose hairs, the 



