82 INVERTEBRATE ZOOLOGY. 



Type IX.— Ascaris lumbricoides. 

 Ascaris mystax. 



The two above species belong to the group of parasitic Nematodes known as 

 " pin-worms " and occurring in the stomach and intestines of Vertebrates. 

 The first named is a large form (20-40"") occurring in man and the pig, and is 

 generally selected as the type of the group. As this is rather difficult to ob- 

 tain, it may be supplemented by ^4. Mystax, common in the cat. and very sim- 

 ilar to the "first, but smaller (4-10™). 



56. External chairicteristics (A. Mystax). For this, use both microscopes 

 according to judgment, the lowest powers first.* Notice the following : — The 

 anterior end is provided with two lateral inng-like jvocesses, giving the whole 

 the appearance of the fluke of an anchor. This is characteristic of the 

 species. The month is situated at the point, surrounded by three oral impil- 

 lae. The posterior end is gently curved in the female, convolute in the male. 

 In both, the anal orifice is a transverse slit, just ventral to the tip. It serves 

 also in the male as a reproductive outlet and is furnished with two minute 

 bristles, or spiculae. Anterior to the anus upon the ventral side there are 

 15-20 papillae. In the female the oviducts open by a single orifice, situated in 

 the mid-ventral line at about the anterior third of the body. 



57. Internal Anatomy. The species Lumbricoides is large and easily dis- 

 sected, but impracticable to use in quantity. A. Mystax may be handled in a 

 small dissecting pan, as in the case of the grasshopper, Type XVIII : or a 

 watch crystal may be used, coated with paraffine, and the parts pinned out 

 with fine insect pins. The body should be opened by a median ventral incis- 

 ion, and the body-wall spread apart. The alimentary canal is a straight tube 

 extending through the center ; it is divisible into an oesophagus, somewhat 

 swollen in its posterior portion, and a chyle-intestine. The rectal jiortion re- 

 ceives in the male the vasa deferentia and may be here termed cloaca. The 

 reproductive organs consist in both sexes of a pair of convoluted tubules, 

 folded back and forth and several times the length of the body. The free end 

 of each is closed, and in this portion the germ-cells are formed. The nephridia 

 are contained in two lateral ridges on the body-wall, which run the entire 

 length of the body. They end by transverse ducts near the anterior end. 



* Hereafter, direetious for simple microscopic procedures will not be given, as the student 

 should now be sufficiently skilled in the use of the instrument to be able to exercise inde- 

 pendent judgment in each case. An exception to this will be made under Type XVIII, which 

 is to be used as a preliminary study. 



