"GROUSE DISEASE " STRONGYLOSIS 



219 



invisible to the naked eye. They live in the caecal portions only of the 

 intestine of the Grouse. The sexually mature females give rise to Deyelo 



I 



FIG. 16. 

 Morulte of eggs. 



their progeny as eggs, which undergo a certain degree of develop- 



ment while still within the body of the worm. By the time they are body of the 



Grouse. 



laid the egg content has become subdivided into a large number of cells, 



forming what is technically known as the morula (Fig. 16). As morulce these 



eggs pass into and mix with the contents of the ceeca, 



all further development thereupon ceasing. This suspen- 



sion of development appears to depend upon a lack of some 



necessary stimulant in the caecal contents, for the eggs 



may be found alive and at the same stage not only 



several days, but even so long as a month after the death 



of the bird. In nature the caeca are evacuated periodically, 



and the ova thus pass out of the body with the soft 



portion of the bird's dropping. In one or two cases where 



a portion of the csecal contents had passed into the rectum, 



and had there become diluted somewhat by the fluid from the 



great intestine, eggs were found to have progressed to the formation of an 



embryo while within the body of a dead bird ; but such a condition is obviously 



abnormal, and does not invalidate the general conclusion that the eggs of this 



parasite require to pass out of the body of the bird before they are able to 



continue their growth, and that, in consequence, the parasites within the body 



cannot increase in number by sexual multiplication. Each and every parasite 



found within the body of the Grouse must therefore have actually entered 



it from the outside. We shall see later that this explains the apparent 



anomaly that whereas practically all Grouse are infected with Trichostrongylus 



only some suffer from the disease. The egg, when newly passed, measures 



0'075 mm. by 0'046 mm. and contains a morula composed of about sixty-four 



cells. 



If a freshly passed csecal dropping be isolated and kept uncontaminated 

 no further development will take place in the ova contained in it. A fungus 

 will gradually grow upon it, and owing to this and bacterial con- 

 tamination the eggs eventually die. If the dropping be exposed 

 to the drying influence of sun and wind, as on the moors during the body - 

 summer, it becomes caked and dry, and the eggs die. If, on the other hand, 

 csecal dropping be spread out in such a way as to admit of the whole becoming 



