104 



How would you dissect Ascaris ? Give a description of its 

 Internal Structure. 



Cut the specimen along each lateral line ; carefully 

 remove the dorsal portion of the body-wall, and pin down 

 the ventral portion. Then proceed to unravel the sinuous 

 tubular reproductive organ or organs, using pins to keep 

 them in position separate from the alimentary canal. 



The mouth opens into a short bottle-shaped gullet or 

 oesophagus. This is followed by a long and flattened 

 mid-gut or intestine which passes straight to the posterior 

 end where it narrows to form a short rectum ending in 

 the anus. 



In the male the reproductive apparatus is a single coiled 

 tube. The first part, the testis, is long and thin ; the 

 succeeding wider portion is the vesicula seminalis, and it 

 ends in a short and thin ejaculatory duct which opens into 

 the cloaca close beside the anus. Two small chaeta sacs,, 

 opening into the cloaca, contain the copulatory spicules. 



in the female the reproductive organs are double. The 

 first and thinnest portions of the two coiled tubes are 

 the ovaries ; the continuous wider portions arc the ovi- 

 ducts, and these pass into still wider uteri. The uteri 

 unite to form the short and narrow vagina which opens, 

 to the outside by the genital aperture. 



In the anterior region, adhering to the body- wall, are four 

 small brown tufts (two on each side), the phagocytic organs. 



Explain the Structure of Ascaris as seen in a Transverse 

 Section of the Body, through the Intestinal Region. 



Beneath the cuticle is the syncytial ectoderm with two 

 slight (dorsal and ventral) thickenings and two prominent 

 lateral thickenings. Each lateral thickening- shows in 

 section an excretory vessel and two nerves. Underlying 

 the ectoderm is the muscle layer. The muscle cells have 

 an elongated form, and chiefly consist of unaltered proto- 

 plasm, the contractile substance being restricted to their 

 outer borders. Some of them show the protoplasm drawn 

 out into a nervous tail connected with the nerve trunk, 

 of the dorsal or the ventral thickening. 



