TRANSFORMATION OF ORGANS OF ANIMALS 33 



pressure of the water, the segmentation has dis- 

 appeared, but across the part corresponding to the 

 exopodite there still remains a transverse groove. 



The second abdominal segment of the female 

 carries appendages similar to those which have 

 just been described. In the male, ' the organs of 

 this segment, as also those of the segment in front 

 of it, have become organs used in fertilization. 

 We must consider what new structures 

 have appeared here, and to what extent 

 these new modifications have been 

 attended by degeneration. The ap- 

 pendage of the second segment (fig. 5) 

 is longer than that of the other seg- 

 ments ; pressed against the ventral 

 surface of the back part of the thorax, 



- ,, i FIG. 5. Astacus 



it stretches out as far as the space be- ftuviatms. Left 



, , ,. . , ,, . appendage of the 



tween the second and third walking 2nd abdominal seg- 



_ , , , . , , ment of the male 



less, the part which corresponds to (fcuitvitvXM/i): 



.-,, .... pr, protopodite; 



the oviduct of the female. It serves as ex, exopodite ; en, 



i i , i ^ a 'T f endopodite; a, 



a channel to conduct the fluid from roiled piate of the 



i i . endopodite; b. 



the male orifice to that of the female, the jointed ex - 



7 . . . tremity of the 



It COnSlStS Of a protopodite (pr.) same (Huxley). 



and an exopodite (ex.) similar to the corresponding 

 parts of the appendages we have just described. 

 The endopodite is profoundly modified. The inner 

 border of its proximal region, which is not jointed, 

 is extended into a thin plate rolled into a hollow 

 horn (a) while the outer border is represented by 

 an annul ated part (b). The part in process of 



C 



