466 Prof. K. Giobben on the Genealogy and 



admit of being traced back to an ancestral form like Apiis, 

 and the Malacostraca probably to one of which a remnant is 

 represented by the Branchipus-ij^^Q. 



That the three Euphyllopod types, which are so different in 

 outward ajipearance, can be regarded as remnants of ancestral 

 forms which presented a general agreement with them, is also 

 conversely again rendered probable by the existence of Crus- 

 tacean groups bearing characters of tliese types in the Animal 

 Kingdom of to-day. The existence of the three Euphyllopod 

 types, BrancMpus^ Apus, and Estheria, and that of Crustacea 

 which are referable to these types, are facts which mutually 

 support one another. 



In order to prove this proposition, I must go somewhat 

 further afield. 



I believe I am correct in stating that Hatschek* was the first 

 to declare that only when a larval or embryonic form of higher 

 animals exhibits a great agreement with the adult stage of 

 lower animals is it possible to conclude with much probability 

 that this corresponds to a similar ancestral form. Thus, we 

 should not be in a position to conclude with a similar show of 

 probability that the Trochosphere larva of the Annelids and 

 Mollusks is a repetition of an ancient ancestral form which 

 resembled it, if there were not still in existence at the present 

 day Rotifers exhibiting great agreement with the Trocho- 

 sphere stage. 



From the existence of developmental stages, which we 

 recognize as of phyletic value, may be drawn the furtiier con- 

 clusion that similar conditions in the form of sexually mature 

 animals must not only have existed during a long period of 

 time, but also must manifestly have enjoyed a wide distribu- 

 tion. The idea that a form of this kind was once widely 

 distributed is again supported by the fact that animal types 

 agreeing with such developmental stages in structure have 

 persisted until the present time. 



From the application of these propositions a further support 

 may be gained for the views which have been developed by me 

 with reference to the origin of the Crustacea. 



If in the existing Animal Kingdom we find three Euphyl- 

 lopod types which are strikingly different in appearance, and 

 all other Crustaceans at present living show certain points 

 of agreement with these three types, then, as it seems to me, 

 additional probability has in consequence been gained, not 

 only for the theory that these three Euphyllopod types re- 

 present remnants of Crustacea which were formerly very 



* B. Hatschek, ' Lehrbuch der Zoologie,' Erste Lieferime-, 1888, 

 pp. 25, 26. 



