14 PROCEEDINGS OF THE NATIONAL, MUSEUM. vol.60 



it and are attached to the inside of the skin itself. They thus servo 

 as stays or supports of these legs, rendering them less liable to 

 collapse. 



INTERNAL MORPHOLOGY. 



General statement. — Inside the skin are found the muscles for 

 moving the body and its various appendages. The digestive system 

 consists of a mouth, an esophagus, usually inclined forv^ard, a 

 straight intestine, and a short rectum. The nervous system consists 

 of two ganglia, one above and one below the esophagus, a ventral 

 nerve trunk, divided posteriorly, and nerves extending to various 

 parts of the body. The reproductive system is made up of paired 

 ovaries or testes, oviducts, or sperm ducts leading back along the 

 lateral margins, cement glands between the oviducts and the body 

 wall, sperm receptacles in the female and spermatophore receptacles 

 in the male. The excretory system consists of a nimiber of small 

 glands distributed in various parts of the body, the ducts leading 

 from them opening to the surface through the skin. 



Musculature. — The most important muscle groups are those in- 

 cluding the longitudinal muscles of the dorsal and ventral surfaces, 

 the muscles which move the various appendages, and tlie dorso- 

 ventral muscles. The largest and longest muscles in the body are 

 two connected with the second antennae. Each is attached to the 

 distal end of the basal joint of the antenna and has its origin near 

 the posterior margin of the cephalothorax. At its origin and for a 

 third of its length it is bifid, then the two branches unite into a 

 single large band. Inside of these muscles in the anterior part of the 

 cephalothorax are two much smaller ones curved like parenthesis 

 marks, which are connected with the first antennae. Behind the 

 origin of these curved muscles on either side are small bundles of 

 fibers which have their origin on the dorsal surface and run down- 

 ward and forward to the base of the mouth tube. Behind these in 

 the posterior center of the cephalothorax are two pairs of narrow 

 longitudinal muscles which run back through the second segment and 

 are attached to its posterior margin. Outside of these in the second 

 segment are two other longitudinal muscles on either side, which run 

 from the first segment through the second into the anterior part of 

 the third segment. From this last point to the middle of the fifth 

 segment there are two pairs of muscles on either side. From the 

 middle of the fifth to the genital segments there are three muscles 

 on either side, and in the posterior part of the genital segment and 

 the abdomen there is only one. 



On the ventral surface there is but a single muscle on either side 

 of the midline, which is broken at places corresponding to the breaks 

 in the dorsal muscles. 



