86 Descriptions of Preparations. 



30. Common Cockroach (Periplaneta Orientalis), 



Female, 



Dissected so as to show its digestive, renal, nervous, and reproductive systems. 



The greater part of the dorsal integ-umental system has been 

 removed by incisions carried along- either side ; the short elytron, 

 the only representative of the wings in the females of this species, 

 has been left in situ on the right side, where it is seen reaching 

 just far enough back to overlap a part of the metanotum; the 

 greater part of the fat body which abounds in the interspaces 

 between the viscera, especially in the abdominal region of these 

 insects even in their adult state, has been removed, and the digestive 

 tract fastened out upon the left side of the body. The upper seg- 

 ment of the digestive canal, seen in this preparation, is the crop, 

 which is about three-fourths of the entire length of the body, and 

 is distended with food. The entire length of the digestive tract 

 would be little more than twice that of the body, and this compara- 

 tive shortness may be considered as compensated for partly by the 

 character of the food of this species, and partly by the large quan- 

 tities which, as seen in this preparation, they devour. A muscular 

 subconical gizzard, an organ which is not developed in the larvae 

 of insects with a perfect metamorphosis such as the Coleoptera, even 

 in species which have it when adult, but is developed in the larvae 

 of Orthoptera, including Libellulidae, follows after the crop. Eight 

 coeca are arranged in a whorl round the commencement of the 'chy- 

 lific stomach,' and a very much larger number of very much longer 

 and more slender tubes are similarly arranged around its lower end. 

 The gizzard does not open directly into the chylific stomach, a 

 narrow neck of about the same length as the gizzard itself inter- 

 vening between the apex of the gizzard and the zone mai-ked out 

 by the eight coeca just mentioned. These coeca appear, from the 

 facts that they often contain a yellowish fluid, and that they never 

 afford lodgment for particles of food even when the digestive tract 

 is distended, to be analogous to the liver of higher animals, whilst 

 the existence of uric acid in the other set of tubules already men- 

 tioned, the so-called ' Malpighian vessels/ would appear to justify 



