6 INTRODUCTION. II. 



easily overcome; but such is not the case; for the alteration of form is frequently, 

 and probably always, so great that two successive conditions cannot be recognized 

 us the same. 1 



When, however, entozoa have been traced to their highest condition of develop- 

 ment, they have always been found to possess well-characterized organs of repro- 

 duction, and the females contain such multitudes of eggs as to render it no longer 

 surprising to find intestinal worms so frequently in vast quantities. The ento- 

 phyta, when fully studied, have been satisfactorily traced to sporules. 



Under the circumstances above mentioned, it is very unreasonable even to sup- 

 pose the necessity of spontaneous generation for animals, which, in such very 

 numerous instances have been proved to possess as great capabilities of reproduction 



1 Thus, almost everybody is familiar with the Gordius, or hair-worm, vulgarly supposed to be a trans- 

 formed horse-hair. The animal is rather common in brooks and creeks in the latter part of summer and 

 in autumn, occurring from a few inches to a foot in length. Its color passes through all shades of brown 

 to black, and it is perfectly hairlike in its form, except that in the wale the tail end is bifurcated, in the 

 female trifurcated (American species). No one has yet been able to trace the animal to its origin ! The 

 female deposits in the water, in which it is found, millions of eggs, connected together in long cords. In 

 the course of three weeks, the embryos escape from the eggs, of a totally different form and construction 

 from the parents. Their body is only the l-450th of an inch long, and consists of two portions; the 

 posterior cylindrical, slightly dilated and rounded at the free extremity, where it is furnished with two 

 short spines; and the anterior broader, cylindrical, and annulated, having the mouth furnished with two 

 circlets of protractile tentaculae and a club-shaped proboscis. No one has yet been able to determine what 

 becomes of the embryo in its normal cyclical course. Those which I have observed, always died a few 

 days after escaping from the egg. 



The grasshoppers in the meadows below the city of Philadelphia are very much infested with a species 

 of Gordius, probably the same as the former, but in a different stage of development. More than half the 

 grasshoppers in the locality mentioned contain them ; but those in drier places, as in the fields west and 

 north of Philadelphia, are quite rarely infested, for I have frequently opened large numbers without finding 

 one worm. 



The number of Gordii in each insect varies from one to five, their length from three inches to a foot ; 

 they occupy a position in the visceral cavity, where they lie coiled among the viscera, and often extend 

 from the end of the abdomen forward through the thorax even into the head; their bulk and weight are 

 frequently greater than all the soft parts, including the muscles, of their living habitation. Nevertheless, 

 with this relatively immense mass of parasites, the insects jump about almost as freely as those not 

 infested. 



The worms are milk-white in color, and undivided at the extremities. The females are distended with 

 ova, but I have never observed them extruded. 



When the bodies of grasshoppers, containing these entozoa, are broken and lain upon moist earth, the 

 worms gradually creep out and pass below its surface. Some specimens which crawled out of the bodies 

 of grasshoppers, and penetrated into earth contained in a bowl, last August, have undergone no change, 

 and are alive at the present time (November, 1852). 



In the natural condition, when the grasshoppers die, the worms creep from the body and enter the 

 earth; for, suspecting the fact, I spent an hour looking over a meadow for dead grasshoppers, and, having 

 discovered five, beneath two of them, several inches below the surface, I found the Gordii which had 

 escaped from the corpses. 



Some of the worms put in water lived for about four weeks, and then died from the growth of Aclilya 

 prolifera. What is their cyclical development? 



The facts presented in this note serve well to show the difficulties in ascertaining the developmental 

 history of entozoa. 



