INVERTEBRATE ZOOLOGY. 121 



may be separated as in the case of the ovary, and found to connect \vith. a 

 small tiibiile, the vas deferens. 



The two vasa deferentia unite below into a common tiibe, as in the case of 

 the oviducts. A mass of coiled white tnbnles lying upon either side, con- 

 nect also with the common tube. How may this mass be resolved? The 

 tubules composing it may be termed prostate tubules and secrete a fluid me- 

 dium in which the minute germ-cells may be suspended. Make a drawing 

 illustrating this system. The finer anatomy of the tnbiiles must be followed 

 by sections, as will be directed later. 



96, Respiratory systevi. In the insect the air is brought into intimate 

 relation to all the organs of the body by a system of tracheal tubes which be- 

 gin at lateral openings (spiracles) and spread everywhere in the form of a 

 branching net-work. There is thus no venous blood, as it is constantly aerated 

 at every point. The disadvantage in this method is that such an animal must 

 remain of small size, for by this means it is impossible to furnish fresh air in 

 large quantities at a distance from the source of the supply. The arrange- 

 ment of spiracles and tracheal tubes in the grasshopper is as follows : 



I. The Spiracles (stigmata). 



These are the breathing-pores through which the respiratory system com- 

 municates with the exterior. There are ten pairs of these in two lateral rows 

 on thorax and abdomen. There are none on the head. 



First Thoracic On membrane between pro- and meso- 



thorax, concealed by the posterior bor- 

 der of the pronotum. 



Second Thoracic (Jn meso-thorax, just dorsal to the 



opening for the articulation of the sec- 

 ond leg. 



First Abdominal On first abdominal tergite at anterior 



margin of auditory membrane. 

 Second— eighth Abdominal On the anterior ventral angle of abdom- 

 inal tergites 2-8. 

 Make an outline drawing of the body as seen from the side. Number the 

 somites and add the spiracles. 



II. Dissection of the respiratory sj'stem. 



Use a fresh specimen, killed by benzine. (If alcohol be used for killing, do 

 not allow the specimen to remain in the liquid.) Open dorsally and pin into 



