Phylogeny of the Organization of the Cestoda. 429 



scarcely intelligible exaggeration when E. Heeckel *, who 

 criticises the phylogenetic relations of the Cestodes in a similar 

 manner, vindicates the merits of von Siebold in having been 

 the first to discover the true explanation and point out the 

 way by which we may be enabled to understand the causes 

 of the ontogenetic phenomena. 



Up to the present only a single exceptional case has become 

 known of a Cestode already sexually mature in the Cysticer- 

 coid state. I allude to the parasite from the body-cavity of 

 the Naidse, described by its discoverer, Ratzel, as Caryo- 

 phyllams appendicidatus, but which was first shown by Rud. 

 Leuckart to be fully sexual and capable of reproduction, and 

 constituted by him the representative of a special genus 

 Archigetes. Although this exceptional case appeared to afford 

 a yet firmer basis to the hypothesis of the renowned helmin- 

 thologist, that the larval stages living in the intermediate 

 hosts were originally the sexual forms, it should nevertheless 

 be far more natural, in view of the relations which we have 

 discussed, to recognize in this case no exceptional survival of 

 a primitive condition, but to interpret it in the light of a 

 secondary transference of sexual maturity to the larval state, 

 just as encysted larval stages of Trematodes (G aster vstomum 

 gracilescens in cysts of Gadus and Distomum agamos of the 

 Gammarinse) may also become sexually mature. 



The designation Archigetes ("ancestor") bestowed by 

 Rud. Leuckart on the parasite of Samuris as the result of his 

 interpretation of it, would apply to our divergent interpre- 

 tation also, in so far as we have in Archigetes a Caryophyllid 

 devoid of the power of proglottid-formation and with simple 

 sexual organs. In this sense, however, it would meet with 

 our approval the more unreservedly, as with it not only may 

 the view of the unsegmented Cestode — in contradistinction to 

 the proglottis — as the equivalent of the Trematode be con- 

 firmed, but also, as a further result, the attempted derivation 

 of the Cestode-body in the foregoing exposition may be com- 

 pletely justified. Moreover, in our at present imperfect 

 knowledge of the development of Archigetes the possibility 

 appears by no means excluded that this interesting parasite 

 also possesses its Gary ophyllaius -stage in the intestine of fish, 

 and only under certain conditions attains to degenetic maturity 

 in the body of Naidse. We may have here a similar dimor- 

 phism to that with which Zeller's excellent work has made us 

 acquainted in the case of Polystomum integerrimum, with its 

 two sexually mature forms — the one on the gills of the tad- 

 pole, the other in the urinary bladder of the frog. 



* E. Haeckel, • Metagenesis und Hypogenesia von Aurelia awita,' 

 Jena, 1881, p. 33. 



