20 ARKIV FÖR ZOOLOGI. BAND 7. N:0 28. 



e. g. in some Antennophorince, where the so-called jugular 

 shields bear the anterior pair of liairs, and the shields are 

 thus morphogenetically equivalent to the anterior pair of 

 Sejus. On the other hand, when the jugular shields ha ve 

 no hairs, which is generally the case, they are not homolo- 

 guous witli those of Sejus, but with the endopodal shields. 

 It will therefore be nessecary to distinguish between these 

 topographically uniform, but morphologically different, shields 

 by giving them different names, and I propose to restrict 

 the use of the name jugular shields to those which are pro- 

 vided with a hair, and consequently homologuous with the 

 metasternal shields, and call the others proeendopodal shields. 



On looking through Berlese's short diagnoses of new 

 genera, w^e find a genus called Asteryiosejus, which, on f urther 

 examination, will probably prove to have a primitive struc- 

 ture of the sternal shield. I quote here B's diagnosis, since 

 it gives a hint as to his opinion as to which is the more 

 primitive. »Sternum abest; sub iugularia derma nudum; 

 sterni tantum fragmenta sunt parvula an te foramen geni- 

 tale.» The expression »fragmenta» seems to indicate that 

 Berlese considers it as due to a retrogressive development. 



If this assumption of the sternal shield originally having 

 been composed of 4 pairs of shields, distinctly separated 

 from one another, and each bearing one pair of hairs, and 

 of the two shields of Sejus, the one of AntenuophoriiicB 

 and the so-called metasternal shields being remnants of this 

 is true, it remains to answer the question of the morphologi- 

 cal value of these shields. 



c. Morpliological yalue of the shields. 



They cannot be real sternal plates, since these are both 

 undivided and odd; moreover, Börner [4. p. 445 — 446] has 

 shown that in the Parasitidce only the tritosternum, i. e. the 

 sternum of the 3rd prosomatic segments exists, consequently 

 the so-called sternal and metasternal plates with their 4 pairs 

 would, if they were real sterria, correspond to segments IV 

 — VI, which is not likely, as it does not agree with the re- 

 gular metameric position of these, w^hich has been proved 

 before. 



