NEMATHELMINTHES 247 



be repeated here, namely, that for the determination of the position of 

 this division a better knowledge of the mode of origin and metamorphosis 

 of their middle germ-layer is most desirable. 



Embryology gives no satisfactory basis for the determination of the 

 position of the Nemathelminthes in the system, and it is hardly possible, 

 in the present state of our knowledge, to decide this. It cannot be deter- 

 mined whether on the one side they have relationships to the Platyhel- 

 minthes or to the Nemertini, and whether on the other to the Annelida. 

 It appears to follow from the structure of the adult animal that there 

 exist resemblances to the organization of the Echinoderes and Gastro- 

 tricha. But the latter are unquestionably related to the Eotatoria, so 

 that in this way relations of the Nemathelminthes to the Trochophore 

 would be brought about (comp. p. 259). 



More obscure still than the position of the Nemathelminthes is that of 

 the Acanthocephali. We have not, as is customary, considered these 

 along with the Nemathelminthes ; it is for the reason that their associa- 

 tion with this group rests upon grounds of purely external nature, and is 

 required neither by their organization nor by the manner of their develop- 

 ment. Even the musculature, which has ordinarily been made use of 

 for the comparison of the two groups, does not appear to be the same in 

 the Nemathelminthes and Acanthocephali either in its arrangement or 

 structure (Safftigen, Koehler [Literature on Acanthocephali, Nos. 6 

 and 31). 



Literature. 



1. BuTscHLi, 0. Zur Entwicklungsgeschichte des Cucullanus ele- 



gans. Zeitschr. wiss. Zool. Bd. xxvi. 1876. 



2. Ganin, M. Ueber die Embryonalentwicklung von Pelodera teres. 



Zeitschr. tciss. Zoul. Bd. xxviii. 1878 (Abstract). 



3. GoETTE, A. Untersuchungen zur Entwicklungsgeschichte der 



Wiirmer. II. Rhabditis nigrovenosa. Leipzig. 1882. 



4. Hallez, p. Recherches sur I'embryogenie de quelques Nematodes. 



Fans. 1885. 



5. Leuckart, R. Die Parasiten des Menschen. Erste Auflage. Leip- 



zig. 1876. 



6. Leuckart, R. Ueber Trichina spiralis. Leipzig. 1866. 



7. Leuckart, R. Neue Beitrage zur Kenntniss des Baues und der 



Lebensgesehichte der Nematoden. Abh. Kgl. sacks. Akad. JViss. 

 Bd. xiii. 1887. 



8. Schneider, Ant. Monographie der Nematoden. Berlin. 1866. 



9. SiEBOLD, T. V. Beitrage zur Naturgeschichte der Mermithen. 



Zeitschr. wiss. Zool. Bd. v. 1854. 

 10. Strubell, a. Untersuchungen iiber den Bau und die Entwicklung 

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