202 M. E. Haase on Abdominal 



(CEcanthus niveus), soon after the segmentation of the blas- 

 toderm, an indeterminate number of paired tubercles are formed 

 upon the abdomen, which exactly correspond to the first 

 traces of the true thoracic legs, but of which only those 

 on the first and last (?) segments are retained for any length 

 of time. 



Further, in 1884, W. Patten observed in a Caddis- worm 

 {Neophylax concinmts) that, when the thoracic legs are about 

 half-grown, a pair of rudimentary appendages are developed 

 upon each of the first three abdominal segments. He also 

 found * that in the embryo of the House-Cockroach (Blatta 

 germanica) a considerable number of abdominal appendages 

 are originally developed, but that they rapidly disappear 

 down to the first pair. 



Finally, V. Graber f has recently recognized within the 

 eight pairs of abdominal stigmata the same number of unde- 

 veloped limb-rudiments, of which the appendages of the first 

 abdominal segment especially, both in their position and their 

 histological structure, were perfectly homologous with those 

 of the thorax. 



From these statements we obtain a fresh support for the 

 supposition that the existing Ilexapoda are to be derived from 

 polypodoas myriopodiform ancestors. 



After Balfour (1880) had adopted this view, the author 

 sought (in 1881) to determine that primitive form of the 

 Tracheata from which both Myriopoda and Hexapoda were 

 to be derived, and came to the result of adopting as such a 

 hypothetical form, nearly allied to the recent order Symphyla, 

 which is represented only by the single genus Scolopendrella, 

 and this he named Protosymphyla. 



The more accurate investigations of last year, specially 

 furthered by B. Grassi's labours, already enable us to attempt 

 the closer definition of the characters of these hypothetical 

 forms by the elimination of such peculiarities as appear to 

 have been acquired secondarily by the existing orders which 

 come under consideration. 



Notwithstanding that in the indefiniteness of the parts of 

 its mouth, the simplicity of its body-segments, &c, it far 

 exceeds all known Tracheata, Scolopendrella itself is to be 

 regarded as a form secondarily developed in several direc- 

 tions, especially degeneratively. Thus its tracheal apertures 

 are confined to the lower surface of the head, its visual organs 

 are aborted, and its thirteenth pair of legs converted into a 

 tactile organ, which yet possesses no ganglion. If the sexual 



* Quart. Journ. Micr. Sci. 1884, p. 48. 

 t Morphol. Jahrb. xiii. (1888;, p. 598. 



