6 REVIEWS. 



commenced several years ago, upon associated entozoa and entophyta, consti- 

 tuting a flora and a fauna within animals ;" and 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 "Des Vegetaux 

 qui croissant sur Vhomme et sur Us 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 



