162 MORPHOLOGY OF INVERTEBRATE TYPES 



the second abdominal somite. The spiracle belongs to the third 

 somite and is situated at its posterior margin. The six embryonic 

 segments situated behind the spinnerets and representing the 

 sixth to thirteenth somites become quite rudimentary, fuse to- 

 gether and form the small anal tubercle at the end of which the 

 anus is situated. 



Appendages. Agelena has two pairs of cephalic, four 

 pairs of thoracic, and two pairs of abdominal appendages. The 

 first pair of cephalic appendages is called the chelicera. They 

 are used for grasping the prey, for holding it during the process 

 of pre-digestion, and, in case of need, for defence. They are 

 two-jointed. The basal joint has more or less the shape of a 

 pyramid, the terminal joint QT fang is thin, pointed, and as hard 

 as steel. When " closed " the fangs rest between the two margins 

 of the basal joints. Both joints move in a transverse plane which 

 is characteristic of all the true or two-lunged spiders. Under the 

 tip of the fang is the opening of the poison duct. The second pair 

 of cephalic appendages is called pedipalpi. They are six-jointed. 

 The first joint or coxa has a maxillary lobe or lamina. It does not 

 seem probable that the laminae serve either for masticating or 

 passing the food to the mouth. The coxa of the pedipalp in 

 tarantulas which "chew" their food, has no lamina, while all 

 true spiders do not "chew" but "suck" their prey. It is more 

 likely that the laminae are tactile organs. Their connection with 

 the process of predigestion will be considered later. The re- 

 maining five joints of the pedipalp form the feeler or palpus. 

 The terminal joint is simple in the female, resembles the terminal 

 joints of the legs and has a claw. In the male, on the other hand, 

 the terminal joint is modified as an organ of copulation. Its 

 structure is very complicated and may be treated here only in a 

 general way. The dorsal wall has more or less the shape of a 

 trough which serves for the protection of the copulatory ap- 

 paratus. The latter is the product of the ventral wall of the 

 terminal joint. It consists of a sperm reservoir inclosed in a thin 

 sac called h&matodocha, an embolus or intromittent organ in the 



