HARDWICKE'S SCIENCE-GOSSIP. 



153 



salivary reservoir is an oval sac with transparent 

 walls, and about half as long again as the gland. 



The ducts and reservoirs have a chitiuous lining, 

 and the ducts exhibit a transverse marking like that 

 of a tracheal tube. 



There are eight (sometimes fewer) csecal tubes 

 arranged in a ring round the fore end of the chylific 

 stomach ; they vary in length, the longer ones, which 

 are about equal to the length of the stomach itself, 

 usually alternating with shorter ones, though irregu- 

 larities of arrangement are common. The tubes are 

 diverticula of Jthe stomach and lined by a similar 



are very numerous (60-70) in the cockroach, as in 

 locusts, ear-wigs and dragon-flies ; and unbranched, 

 as in most insects. They are about '8 in. in length, 

 and '002 in. in transverse diameter, so that they are 

 barely visible to the naked eye as single threads. In 

 larvae about \ of an inch long, Schindler (Zeitsch. f. 

 wiss. Zool. Bd. XXX.) found only eight long tubules, 

 the usual number in Thysanura, Anoplura, and 

 Termes. In the adult cockroach the long threads 

 wind about the abdominal cavity and its contained 

 viscera. 



In the wall of a malpighian tubule there may be 



Fig. 81.— Transverse section of wall of chylific stomach of cockroach, showing epithelium and glandular cells. To the left side 

 the epithelium is removed, to show the connective tissue skeleton. X 325. 





Fig. 82. — Transverse section of rectum of cockroach. X 50. 



•U- 



Fig. S3. — Free end of a single 

 epithelial cell of chylific stomach, 

 showing processes. X 3000. 



epithelium, but do not contain any undissolved food. 

 In the living animal they are sometimes filled with a 

 whitish, granular fluid. They are developed late, 

 and are absent or of inconsiderable size in larval 

 cockroaches. 



The position of these coeca suggests a comparison 

 with the tubular "liver " of Crustacea, and with the 

 pyloric caeca of fishes, but no adequate physiological 

 investigation has been made as to the function of any 

 of these organs. 



The malpighian tubules mark the beginning of the 

 small intestine, to which they properly belong. They 



distinguished (i) a connective tissue layer, with fine 

 fibres and nuclei ; within this, (2) a basement-mem- 

 brane, between which and the connective tissue layer 

 runs a delicate, unbranched tracheal tube ; (3) an 

 epithelium of relatively large, nucleated cells, in a 

 single layer, nearly filling the tube, and leaving only 

 a narrow, irregular central canal. Transverse 

 sections show from four to ten of these cells at once. 

 The tubules appear transparent or yellow-white, 

 according as they are empty or full ; sometimes they 

 are beaded or varicose ; in other cases, one half is 

 coloured and the other clear. The opaque contents 



