SUPPLEMENT. 403 



College, on the Entozoa, I quoted (substantially) from Dr. Rob- 

 erts, as follows : 



" A marvelous light has been thrown in recent years on the 

 zoological position of the Entozoa, chiefly by the researches of 

 Siebold and Van Beneden. It has been ascertained that the hy- 

 datid worm found in man, constitutes the encysted phase in the 

 developement of a very minute tape- worm which infests the 

 dog. The tape-worm in question is the Tcenia echinococcus ; the 

 entire adult animal is so small that it scarcely exceeds the size 

 of a millet seed. It consists of but three segments, of which 

 three, the last only is fruitful. When this segment arrives at 

 maturity, it is cast off, and a new one developed in its place. 

 Myriads of these worms are sometimes found in the intestine of 

 the dog, and their eggs are discharged in countless numbers 

 with the excrements, the eggs so discharged are scattered far 

 and wide ; and some of them find their way with the food into 

 the stomachs of men and other creatures suitable for their de- 

 velopment. Arrived there, the embryo is liberated ; and after 

 penetrating the mucus membrane, it burrows its way, or is car- 

 ried by the blood current to some distant organ, where it is 

 arrested. Having thus lodged itself, it presently reappears as a 

 hydatid vesicle, in which are developed the echinococci, as be- 

 fore explained. Dogs in their turn become infested with the 

 corresponding tsenia by feeding on the offal of slaughtered 

 sheep, pigs, etc., which had been infested with hydatids. The 

 echinococci therein contained develop in their intestines into 

 thetsenia echinococci, and thus the circle of transformation and 

 development recommences." 



By similar cycles of transformation and development, do we 

 arrive at a class of parasites known in medicine as the ectozoa. 

 This term may be said to include, or be applied to, worms or 

 larvae of insects that have been introduced into the intestinal 

 canal by accident. Animalcules, such as the hair worm, grub 

 of the fly, may be mentioned ; also the larva of the bee, the spi- 

 der, etc. Among animals, the disease known popularly as the 

 botts, to which the horse is frequently a victim, is caused by 

 such animals swallowing the ova of the oestrus or gad-fly. 



That oleomargarine manufactured from refuse animal fata, 



