144 DESCRIPTIONS OF PREPARATIONS. 



i 



of gland cells with large ramified nuclei, and internally a porous chitinoid (?) 

 membrane. The secretion contains (i) yellow-brown globules, which if numerous 

 make the vessels opaque; (2) clear white globules; (3) uric acid crystals. The 

 tubes open in Periplaneta into the lower portion of the chylific stomach, but in 

 most Insecta into the intestine. Rathke, however, states that in Blatta Germanica 

 they arise as outgrowths from the intestine. 



The corpus adiposum, or fat body, is a whitish glistening tissue, arranged more 

 or less in masses, and consists of cells containing oily drops, albuminous bodies, 

 and in some cases uric acid. This tissue originates by proliferation from a layer of 

 cells within the hypodermis, if the observations of Wielowicjski on Corethra are to 

 be trusted. Sub-hypodermic cells have been described also by Viallanes in the 

 larval Eristalis and Musca. 



If the abdominal terga are removed as a connected piece, the heart and 

 surrounding tissues may be found on its inner surface. The heart consists of a 

 tube, divisible into an anterior aortic membranous portion, which runs forward into 

 the thorax, and a posterior muscular portion ending blindly behind, and divided 

 into a series of chambers by lateral apertures. Its muscles are arranged circularly 

 or spirally, and at the apertures in a figure of oo . The apertures are valved. The 

 chambers contract successively from behind forward, and according to Cornelius, 

 there were eighty such contractions in a minute in a Blatta which had just undergone 

 ecdysis. The heart is suspended to the back of the abdomen by muscular fibres. 

 Its walls are connected to a network of elastic fibres and interposed pericardial 

 cells, which resemble the cells of the fat body, and the whole is limited on the 

 surface turned to the viscera by a tissue partly fibrous and partly composed of the 

 paired alary muscles. These muscles are striated, and arranged segmentally in fan- 

 shaped bundles. The handle of each fan is attached laterally to one of the terga ; 

 its expanded portion is spread out below the heart, and the muscle-fibres end in 

 tendons reticularly arranged. The whole structure, as pointed out by Graber, 

 forms a pericardial sinus, which expands and contracts rhythmically like the heart. 

 Numerous tracheae ramify in it and upon the heart. A very similar structure, 

 with alate muscles, covers over the ventral nerve cord, and forms a pulsating sinus, 

 but the contractions run from the anterior to the posterior extremity. 



There are nine stigmata, or respiratory apertures, two thoracic, and seven 

 abdominal. According to Bela Deszo, the stigmata and apertures into the heart 

 correspond numerically in Insecta, Mynapoda, and Arachnida. This statement 

 can, however, only be true as far as concerns the abdominal stigmata. The two 

 thoracic stigmata are situated, one in the meso-, the other in the meta-thorax, in 

 front of the articulation of the coxa. The abdominal stigmata are placed immedi- 

 ately under the lateral expansions of the terga, upon conical papillae. With the 

 exception of the first, these papillae are concealed by lateral prolongations of the 

 sterna. The last of the series is the largest. The entrance into the trachea, which 

 rises from each stigma, is protected (i) by hairs which cross the aperture, (2) by a 

 special apparatus for closing the tube, which in the Orthoptera is continuous with 

 the lips of the stigmatic aperture. These lips are prolonged inwards as two valves. 

 A process arises on the outer, i.e. visceral surface of each of these valves. A 

 muscle passes from one to the other process round one of the margins, and when it 

 contracts, squeezes the valves together, and thus narrows the aperture. The details 



