If the part of a rabbit or hare infected by a Pentastomum denticulatum be eaten by a dog or wolf, the parasite passes into the nasal cavity of the latter, and after further changes of cuticle becomes a fully developed sexual Pentastomum tænioides, which does not differ to any very marked extent from P. denticulatum.
In their general characters the larval migrations of Pentastomum are similar to those of the Cestodes.
The internal anatomy of the adult Pentastomum, as well as the characters of the larva with two pairs of clawed appendages, are perhaps sufficient to warrant us in placing it with the Arthropoda, though it would be difficult to shew that it ought not to be placed with such a form as Myzostomum (vide p. [369]). There do not appear to be any sufficient grounds to justify its being placed with the Mites amongst the Arachnida. If indeed the rings of the body of the Pentastomida are to be taken as implying a true segmentation, it is clear that the Pentastomida cannot be associated with the Mites.
Bibliography.
(539) P. J. van Beneden. “Recherches s. l’organisation et le développement d. Linguatules.” Ann. d. Scien. Nat., 3 Ser., Vol. XI.
(540) R. Leuckart. “Bau u. Entwicklungsgeschichte d. Pentastomen.” Leipzig and Heidelberg. 1860.
Tardigrada.
Very little is known with reference to the development of the Tardigrada. A complete and regular segmentation (von Siebold, Kaufmann, No. [541]) is followed by the appearance of a groove on the ventral side indicating a ventral flexure. At about the time of the appearance of the groove the cells become divided into an epiblastic investing layer and a central hypoblastic mass.
The armature of the pharynx is formed very early at the anterior extremity, and the limbs arise in succession from before backwards.
The above imperfect details throw no light on the systematic position of this group.
Tardigrada.