REVIEWS. 7 



length. Its colour passes through all the shades of brown to black, and is perfectly 

 hair-like in its form, except that in the male 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 is found millions of its eggs, 

 deposited in long chords. 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 1 -450th of an inch long, and consists of two portions ; the posterior cylin- 

 drical, 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 retractile 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 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 rarely infested. 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 colour, and undivided at the extremities. The 

 females are distended with ova, but I have never seen them extruded. 



" When the bodies of grasshoppers, containing those entozoa, are broken and laid 

 upon moist earth, the worms gradually creep out and pass below its surface. Some 

 specimens which crawled out of the bodies of grasshoppers, last August, have under- 

 gone 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. Some of the worms, put in water, lived for about four weeks, 

 and then died from the growth of Achlya prolifera. What is their cyclical 

 development ?" 



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

 history of entozoa. 



After some preliminary inquiries into the nature of life in general, Dr. 

 Leidy proceeds to the consideration of the topics more immediately bearing 

 upon the nature and origin of entozoa, and into phytic life. Interesting 

 as these topics are, and important, as bearing upon a class of questions 

 which, at the present period, closely occupy the attention of the naturalist, 

 we must pass them by, merely directing our reader's attention to their con- 

 sideration in the pages of the present memoir, recording the result of some 

 of the interesting researches of our author. 



Entozoa may and do penetrate through the living tissues ; but it is entirely 

 by the mechanical process of boring. 



The intestinal canal of animals is most frequented by ento-parasites, on 

 account of the ease with which the germs enter with the food. 



Aquatic animals are more troubled with entozoa than those which are 

 terrestrial, because the water gives a better medium of access than the air. 



Terrestrial animals are more infested with ecto-parasites, because their 



