II.] THE CRAYFISH AND LOBSTER. 207 



dead-white tube, immediately external to c. In the 

 female; a short membranous tube, only visible at 

 this stage with difficulty. 



e. The digestive gland; a yellow pulpy-looking mass, 

 filling up the interspaces in the cephalothorax ; it 

 is most obvious in front of the genital apparatus. 



f. The excretory organ (green-gland); a paired delicate 

 green structure, lying, at a low level, in the extreme 

 anterior end of the cephalic cavity. It can be at 

 once seen on slightly displacing the stomach. 



g. Note, incidentally. 



o. The adductor mandibuli muscle; a large oval 



fleshy mass, lying immediately external to the 



stomach (cf. Sect. C. $d.). 

 y8. The extensor abdominis muscle; its cut ends will 



be found, attached to the thoracic epimera. 

 y. The gastric muscles ; passing from the stomach to 



the adjacent exoskeleton (for details see Sect. E). 

 8. The integument (hypodermis) ; a delicate dark red 



layer, lying immediately under cover of the 



exoskeleton. 



e. The body-cavity; obvious as an ill-defined chamber, 

 within which the various organs of the viscera are 

 contained. 



f. The respiratory organs ; seen lying within the 

 branchial chamber ; they are exclusively thoracic. 

 Follow the cut edge of the branchiostegite. 



E. The alimentary organs. 



1. Dissect from the tergal aspect, as directed for Sect. D., 

 and remove the heart and reproductive apparatus. 

 Examine — ' 



