238 W. WESCHE ON THE MALE GENITALIA OF THE COCKROACH, 



to be an articulation (Figs. 1, 2, v, and 7). Membranes connect 

 the spinus with the theca and hypophallus, and enclose this piece 

 (Figs. 1, 2, h). 



If we indulge our imagination, we can form a mental image of 

 some annulated, worm-like creature, low in organisation, scarcely, 

 if at all, higher than a colony of polyps ; each annulation com- 

 plete in itself, with alimentary canal, genital pore, and some 

 form of rudimentary appendages. The genital pore, as we have 

 found in the majority of creatures, would be on the side opposite 

 the oral aperture. That being so, at one end of this compound 

 worm would be a mouth and at the other a pore. These, from 

 their favourable situations, monopolised the work, and the others 

 atrophying from disuse, or, if part of the alimentary canal, 

 joining on to the mouth of the next segment, evolved into a worm 

 which was compound only in the number of its appendages and 

 annulations, and would be rather lower in the scale of life than 

 Peripatus. From this we can see why the ovaries and testes of 

 insects are always found at the posterior end. It also explains 

 in some measure the anomalous genitalia of the male dragon-fly 

 (Odonata). 



To continue our phantasy, in the course of ages, one or more 

 sets of the appendages were used at both extremities, either to 

 grasp food or to hold a partner in coitus. Slowly and by degrees 

 modifications in the appendages, which were of advantage to the 

 parent, were transmitted to the offspring and became established, 

 until finally the appendages of a number of segments were brought 

 into use and were changed into hooks, blades, and feeling-organs, 

 grouped round the mouth at one end and the pore at the other. 

 A fold of skin in the median line was also modified, either into 

 a hook or a protection of the important apertures. These folds 

 are now represented by the single unpaired organs which are 

 found both in the mouth and the genitalia. In the former it is 

 the lingua, in the latter the spinus titillatorius. Such is the 

 theory which has been put forward to explain how the com- 



