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ART. XXVI. — Descriptions of two species of Distoma with the partial history of one 

 of them. (Plate 43.) By Joseph Leidy, M. D. 



One of the most remarkable divisions of organized nature, and that which probably 

 more than all others has at once excited the wonder, disgust, and horror of mankind, 

 is the class of animals known as Entozoa. Their habitation, frequency of occurrence 

 and numbers, and their often terrific appearance, are sufficient reasons to have given 

 rise to such feehngs. From the great variety and singularity of their form, their 

 habits, and the mystery in which their origin and progressive development has 

 always been involved, they have ever caused naturalists to attach peculiar interest to 

 them, and they have been studied with a patience and zeal which has not been 

 excelled in any other branch of human learning. 



In the term Entozoa has been included many animals of very different zoological 

 characters, but in the present state of our knowledge, the general distinction founded 

 upon the character of their habitation is probably as good a classification as can be 

 adopted. 



We are often astonished at the extent of ecto-vitality : at the idea of a drop of water 

 from any stagnant pool containing as many living bodies as there are human beings 

 on the globe, etc., yet when we consider closely ecto-vitality, we will probably be 

 no less astonished at its extent. Thus, when we reflect upon the ^moving mass 

 containing millions upon millions of Bodo, in the large intestine of the toad, frog, 

 salamander, in the intestine of the house-fly, &c. ; the innumerable hosts of 

 monads, vibrios, &c., in the intestinal and other fluids of most animals ; the infinity 

 of spermatozoids ; the numerous Gregarince in the ventriculus of insects we may 

 suspect internal and external life almost to be in equilibrio in their extent. But it is 

 not only the lowest forms of entozoa which are so numerous : I have removed fifty-six 

 specimens of Distoma from the pericardial cavity of a snail ; I have preserved over 

 six hundred specimens averaging the one-tenth of an inch in length of a nematoid 

 worm which I took out of the abdominal cavity of two individuals of Passalus 

 cornutus ; from a single Julus marginatus I obtained 140 specimens of Gregarina, 

 78 of an Ascaris, 27 of another nematoid which I have named Aorurus, over 1000 of 

 Nyctotherus, besides innumerable monads, vibrios, and entophytes. My friend Dr. 

 J. L. LeConle informed me he had seen a pint of Ascarides taken from the intestinal 

 canal of a Boa constrictor. I found at one time fragments of 80 specimens, averaging 



