396 ENTOZOA. 



I recapitulate the experimental data by wticli lie has satisfactorily 

 proved that the Pentastoma denticulatum is merely the larval or 

 sesuaUy-immature condition of Pentastoma tcenioides. My own few 

 experiments on this score were only attended with negative results ; 

 but Leuckart's testimony is conclusive. I have already, indeed, in 

 the pages of the "Microscopical Journal " (Vol. vii. p. 182), given 

 an abstract of one of his earlier papers on this subject, and there- 

 fore I need here only adduce such of the results as seem necessary 

 to throw light upon the general features of this parasite and the 

 metamorphoses which it undergoes. To be brief, Leuckart re- 

 cognizes four well-marked stages of development. First, the 

 embryo with a boring apparatus. Schubert correctly described it 

 also as having two pairs of lateral appendages or feet, each of 

 these being supplied with two claws ; it has likewise a caudal pro- 

 longation nearly equal in length to the rest of the body. Yan 

 Beneden gives a very similar description (Bull, de I'Acad. Eoyal 

 de Belg., xv., 1848), and, from my own examinations, I can offer 

 similar testimony. The second stage is that in which the embryo 

 has become transformed into a motionless pupa. The third is 

 the ordinary larval condition (= Pentastoma denticulatum) charac- 

 terized by numerous rows of small tooth-like spines in addition to 

 two pairs of double claws. The fourth is the sexually-developed 

 stage, furnished with a simple hook-apparatus, and unsupphed 

 with integumentary denticles. " Our Pentastomes, therefore," 

 says Leuckart, " exhibit two kinds of larval forms, an earlier and 

 later one, as takes place in other animals ; this also occurs even 

 in insects (Strepsiptera and Meloidce) ; only that, in our case {i.e. in 

 Pentastoma), both do not immediately follow one another, but are 

 separated by a resting condition, which I have designated as the 

 pupa stage. In choosing this name I do not mean to express a 

 complete identity of this intermediate state with the pupal sleep 

 of insects." 



As it is only the encysted and larval conditions that are to be 

 met with in the human body, I now proceed to notice these more 



