56 



INTERNAL ANATOMY. 



Technical note. — With fine scissors cut open the body 

 along the median line of the dorsum, cutting through only 

 the body-wall. Put the specimen in a dissecting * dish, pin 

 out the cut edges with ribbon pins and cover with water. 



Adipose tissue. — The most conspicuous organ in the 

 opened body-cavity is the alimentary canal extending as a 

 long thick tube longitudinally from head to caudal extremity. 

 It is nearly entirely enclosed in a thin, whitish, perforated 

 sheet of adipose tissue, or fat. Note the disposition of this 

 sheet. Examine a small piece in water on a slide under the 

 microscope, first under low power and then under higher 

 power. Make a drawing showing the structure of adipose 

 tissue as thus shown. 



Alimentary canal and accessory parts. — The aliment- 

 ary canal is composed of a series of successive regions or 

 parts ; first (foremost) the slender oesophagus, embraced by 

 the circumxsophageal nerve commissures with the small white 

 brain lobes above ; second, an abruptly dilated conical part, 

 the proventriculus J third, a part immediately behind this and 

 not sharply marked off from it, the elongated ventriculus 

 bearing at its anterior end four elongated pouches, the gas- 

 tric cceca. In the sheet of adipose tissue surrounding the 

 ventriculus several slender convoluted thread-like processes 

 may be seen ; these are the Malpighian tubules, the organs of 

 excretion, four in number. They arise from the alimentary 

 canal just back of the ventriculus at a part marked by a pale 

 transverse line. Behind this line is a fourth part of the ali- 

 mentary canal, the small intestine. It is of smaller caliber 

 than the ventriculus and opens into a succeeding part of the 

 canal, the large intestine, near its anterior end. The large in- 



* "s^or directions for making dissecting dish see pp. 34-35. 



