74 



G. J. de Fejervary: 



separably attachedto or fused with the primary dermal bones 

 in both the European species pertaining to this Genus (P. fuscus 

 Laur., and P. cultripes Cuv.Y^), so that the shape of the primary 

 dermal bones can only be examined in young specimens, a mecha- 

 nical removal of the secondary exoskeletal elements, occurring in 

 the adult, being quite impossible. As showTi in Figs. 1 — 2 the 

 secondary exoskeletal bones attained in P. cultripes Cuv. a con- 

 siderably higher development than in P. fuscus Laur. 



Figvire 1. Figiire 2. 



The course of the development of this secondary exo- 

 skeleton seems to be most simply explainable. The lime of the 

 derm (cutis or corium) forms at the beginning smaller concretions. 

 which, in the lapse of time, coalesce between each other, forming 

 larger plates. Ihe shape of these plates depends on the local 

 anatomical structures of the respective regions of the corium, as 

 well as on the mechanical action produced by the kinesis of the 

 animal, and on the effects produced b}^ oecological conditions, i. e. 

 by the environment. At the beginning the dermal ossifications 

 occurring on the skull seem to be limited to those regions of the 

 derm which cover osseous surfaces, i. e. which are immediately 

 super posed to the bones constituting the roof of the skull. Almost 

 all of these latter bones are primary dermal bones, and only very 

 few pertain to cartilaginously preformed bones, as the ethmoid 

 for instance. It is a well known fact that in Batrachians and Reptiles 

 the skin generally very closely adheres to the roof of the skull, 

 and so the lime-concretions formed' by the derm on these parts 

 coalesce very soon with the bones immediately beneeth them, 

 constituting thus a socalled ,,crusta calcarea". 



If the secondary dermal ossification continues to a higher 

 degree, it may form osseous bridges, connecting various prominent 

 points or edges of oppositely neighbouring bones. In P. fuscus, 



membrane bones, or at least membranes which have received their bone 

 from the cutis, this superimposed ossifying mass of Pdohates is a second 

 iiistalment, or second generation of dermal bone," 



And surely also in the Asiatic P. syriacus Bttgr. 



