LITERATURE. 137 



would be still greater if a six-limbed larva also appeared in 

 Pentastomum, as was maintained by De Filippi. Unfortunately, 

 but little reliance can be placed upon this otherwise important 

 statement, as may be seen from a glance at his figures. A direct 

 comparison of the Pentastomum larva with an Acarid larva is 

 inadmissible on account of the absence of mouth -parts in the 

 former. In this case degeneration may, indeed, have gone even 

 further than in the Acarina, and it is possible that Pentastomum 

 may be derived from forms resembling these latter animals. Certain 

 Acarids, e.g., the Pliytopta, in which two pairs of limbs disappear, 

 and in which the body is lengthened (pp. 107 and 108) might 

 be regarded as indicating the possible line of origin of a form 

 like Pentastomum (Leuckart). But it must be expressly pointed 

 out that there is no definite ground for this view, and that 

 Pentastomum might, with almost equal justification, be derived 

 from some other group of Arthropoda. Unfortunately, the organi- 

 sation of the adult also fails to afford any definite clue, but only 

 makes it clear that Pentastomum is a form much reduced by 

 parasitism. Important systems of organs, such as the respiratory 

 and excretory systems, which elsewhere, by their characteristic 

 development, help to determine systematic position, are wanting. 

 A distinct blood vascular system also is not developed. In the 

 transversely striated musculature, on the other hand, we have an 

 Arthropodan character, and it has already been pointed out that 

 the genital organs can, perhaps, be interpreted in this sense. The 

 ovary in its structure recalls that of the Arachnida, the eggs 

 bulging out like follicles on its surface, and giving the organ an 

 aciniform appearance. 



LITERATURE. 



1. Bexedekt, P. J. van. Recherches sur l'organisation et le 



developpement des Linguatules (Pentastoma). Ann. Sci. Nat. 

 (3). Zool. Tom. xi. 1849. 



2. Filippi, F. de. Nuova linguatula con embrioni di particolar 



forma. Archiv. Zool., Anat. e Fisiol. Fasc. i. Tom. i. 

 Genova, 18G1. 



3. Gerlach, A. C. Pentastomum denticulatum bei zwei Ziegen. 



Jahresber: d. 1c. Thierarzneischule zu Hannover, ii. 1869. 



4. Hoyle, W. E. On a new species of Pentastomum (P. protelis), 



from the Mesentery of Proteles cristatus, etc. Trans. Roy. 

 Soc. Edinburgh. Vol. xxxii. 1887. 



