ANIMAL PARASITES 



37 



7?eee/r>taek 



TZetrctctorS 



Brvrtrt 

 Retinaculum 



Cement 

 </ai7c£s 



host, increasing in size and finally returning to the intestine to 

 mature. 



Using this species or the related Toxocara from the cat or dog, 

 make a series of sketches of first, the unsegmented eggs from the 

 uterus; and second, various segmentation stages from eggs which 

 have been incubated at summer temperature for a few days. 

 The eggs are not infective until they have reached the coiled 

 embryo stage. In both Ascaris lumbricoides and Toxocara cants 

 (Belascaris marginata) this requires upwards of 2 weeks. 



Examine the demonstration 

 specimens of Ascaris larvae in the 

 tissues of the liver (Fig. 14) and 

 lungs of experimentally infected 

 rats. If available, note the evi- 

 dences of "Ascaris pneumonia" in 

 an animal which has been fed in- 

 fective eggs of the worm about a 

 week previously. 



Demonstrations of Gordiacea 

 and of Acanthocephala. — Com- 

 pare your specimen of Ascaris, a 

 typical nematode, with the demon- 

 strations of representatives of the 

 Gordiacea and the Acanthoceph- 

 ala. 



The Gordiacea are the so-called 

 "hair-snakes." Their bodies are 

 slender and wire-like and lack an alimentary canal in the adult 

 stage. In this stage they are free-living, but in the larval stage 

 they are parasitic in insects and less frequently "in other inver- 

 tebrates. As parasites of grasshoppers they often play a part 

 in the natural control of these pests. 



The Acanthocephala (Fig. 15) are characterized typically by 

 the presence of a protractile proboscis, armed with numerous 

 hooks, and by the lack of an alimentary canal. The larval stages 

 are found in crustaceans, insects, fish, and small mammals. 

 Adults are especially abundant in birds and fish. The demon- 

 stration specimens are of M acrocanthorynchus (Echinorynchus) 

 gigas, a common parasite of hogs. Note also the demonstration 

 of eggs, which are 90 to 100 n long, nearly cylindrical, with a 

 three-layered shell, the outer layer of which is marked by numer- 

 ous depressions suggestive of those of an almond shell. 



Fig. 15. — Acanthoccphal us raniv 

 of frogs and salamanders. {After 

 Van Cleave.) 



