6 
REVIEWS. 
commenced several years ago, upon associated entozoa and entophyta, consti¬ 
tuting a flora and a fauna within animalsand though, perhaps, to the 
over-fastidious such a record may reveal unwelcome truths as to the presence 
of some fellow-lodgers, whose existence they would gladly ignore—and 
though these may rank among the lowest form of organization we are 
acquainted with—they still surpass the loftiest efforts of man, and place all 
his wonted skill at nought, forcing him to confess that, insignificant as 
they are, they can never be imitated successfully by him—that they bear 
about with them that which is God’s prerogative to give—life ; and in their 
examination “ he will be led to understand a little of the meaning of God’s 
glorious title— maximus in minimis .” 
Dr. Leidy’s able memoir opens with an introduction, in which the lead¬ 
ing facts connected with the entozoa—or animals living within other 
species; and entophyta—or vegetable parasites within animals—are skillfully 
reviewed. The former of these have, from the most remote time, attracted 
attention on account of the peculiarity of their position, the unpleasant 
ideas associated with them, the sufferings they frequently induce, and the 
difficulty of explaining their mode of origin. The existence of entophyta, 
on the contrary, from their minute character, long remained unknown, until 
the microscope of Leuwenhoek detected the algoid filaments of the human 
mouth ; and it is only within a comparatively recent period that any large 
number have been discovered. In the year 1847, a very interesting mono¬ 
graph of these appeared at Paris, by Robin, under the title of u Des Vegetaux 
qui croissant sur Vhomme et sur les animaux vivant.” In tracing the 
history of these curious parasites, modern observations would indicate that 
both entozoa and entophyta are produced from germs derived from parents 
having a cyclical development. The difficulty of tracing the progress 
of this development is very great, “ particularly in the case of the 
entozoa, whose various stages of existence are passed under totally different 
circumstances ; sometimes within one organ and then another of the same 
animal ; sometimes in several animals ; and at other times quite indepen¬ 
dent of, and external to, the animals they infest. If, however, an entzoon 
preserved the same form throughout its migrations, the difficulty just men¬ 
tioned would be easily overcome ; but such is not the case, for the alteration 
of form is frequently and probably always so great, that two successive con¬ 
ditions cannot be always recognised as the same.” As a familiar example 
of this, we may mention the case of the Gordius , or hairworm, vulgarly 
supposed to be a transformed horse hair. 
“ This animal, says our author, is rather common in brooks and creeks in the 
latter part of summer and autumn, occurring from a few inches to a foot in 
