and penis of insects. In the female each entire nemic 

 ovary is compared to a single unit of the insect ovary; 

 reduction in number of ovarian tubules is cited as evi- 

 dence of relationship, such reduction having been re- 

 ported by Cholodowsky (1908) in the dipteran, Thcria 

 muscaria Meig. Finally Seurat differed with Biitschli 

 (1876) in that he homologized the lateral canals with 

 the serii;igenous glands of microgasters rather than with 

 trachea. He pointed out the fallacy of Rauther's compari- 

 son of the triradiate pharynx of Anopheles larvae, Seurat's 

 argument being that the three muscle bands or sectors 

 extend from the body wall to the extei-nal surface of the 

 pharynx and are hardly comparable to the radial muscles 

 of nemic esophagi ; rarity of the occurrence of a stylet 

 in free-living nemas and its obviously secondary adaptive 

 function in feeding were pointed out as evidence of the 

 lai:k of phylogenetic significance of stylets. Seurat then 

 asked, if in the presence of the evidence, one must not 

 think of the primitive nematode as being a larva of the 

 Holometabola adapted to detriticolous life, having lost 

 all segmentation, become adult and sexual after having 

 fulfilled its normal molts 'but preserving infantile char- 

 acters. As a parallel instance of neoteny, the coleopterous 

 malacoderm, Phengodes, according to Haase (1888), has 

 a larval female possessing normally constituted genitalia 

 and producing fertilized eggs. As contrary evidence 

 Seurat cited the following differences between nematodes 

 and insects: Absence in nematodes of. any trace of seg- 

 mentation or articulate appendages and anything- cor- 

 responding to the trachea, as well as the divergence in 

 cleavage of the egg. (The latter he felt could be explained 

 through the presence of an abundance of yolk in the 

 Insect egg). 



Baylis (1924) reviewed the theories extant and con- 

 cluded that nemic-insect (arthropod) relationship is prob- 

 able on the basis of the common cuticular esophageal 

 (pharyngeal) lining, malpighian tubule-rectal gland 

 homology, tubular form of gonads, homology of penis 

 and spicules, metameric arrangement of setae in nema- 

 todes, common absence of cilia, paedog-enesis of insect 

 larvae, and molting. More recently (1938) Baylis ex- 

 pressed the view that the origin of nematodes is un- 

 certain, perhaps in a very remote period nematodes and 

 arthropods had a common ancestor but it would be un- 

 wise to press the suggestion since at the present time 

 we do not know whether the conditions exhibited by 

 dipterous larvae are primitive or secondarily adapted. 



It will be seen from the above resume that of all of 

 the proponents of common nemic-arthropod relationships, 

 Biitschli alone proposed a theory of descent presuppos- 

 ing direct rather than regressive evolution and he placed 

 the Tardigrada as primitive arthropods. The majority 

 of Seurat's points would be as acceptable to the concept 

 of progressive as to the concept of regressive evolution. 

 Paedogenesis might be even considered an atavistic ten- 

 dency of insects. It would still be necessary to account 

 for the origin of aquatic arthropods in order to accept 

 progressive nemic-arthropod relationships but such an 

 explanation is entirely unnecessary to the regressivists. 



4. ScoLECiDAN (Pkotonephridial) THEORY. As previ- 

 ously noted, this theory is traceable directly to Huxley 

 (1856) but it has undergone many modifications both by 

 the original author (1864, 1878) and by other workers, 

 the chief of whom was Biitschli (1876). This theory in 

 substance, provides for the union of all "unsegmented 

 worms" in one superphyletic group just above the coelen- 

 terates and ctenophores. All higher forms of life are 

 supposed to have arisen from lower ancestral (primitive, 

 extinct, rhabdocoele or rotatorian-like) scolecidans. Such 

 a view presumes phylogenetic significance of the trocho- 

 phore larva and is very close to the consensus of present 

 day zoologic opinion. Disagreements relate to the subdi- 

 vision of the "Scoleeida" into its major series, phyla and 

 classes. 



Haeckel (1872, 1896) revised the Animal Kinj-dom on the 

 basis of his "Gastraea Theory" placing the forms with 

 neither body cavity nor anus in the Acoelomati; he ac- 

 cepted the common Platyhelminthes (renamed Platodes) 

 grouping (Turbellaria, Trematoda, Cestoda) consider- 

 ing the platyhelminths as icoelenterates and for them 

 hypothesizing a simple gastrula-like ancestor with pro- 

 tonephridia. The Acoela were placed as the most primi- 

 tive living worn.s and the Rhabdocoela as an'-estors of 

 all higher animals. Such an ancestral form is described 



as having two testes and two ovaries, a muscular stoma, 

 no anus, a parenchymatous body cavity, an epithelial 

 brain and an incompletely differentiated mesoderm. The 

 formation of a body cavity, according to Haeckel, should 

 be considered as a regression from a previously p ren- 

 chymatous state. In his earlier revision (1872) he listzd 

 Rotatoria and Nematoda in the Coelomati. Later he re- 

 vised this group into the "True Vermes" compo sd of the 

 following phyla: 1. Rotatoria (with Gastrotricha as old- 

 est and in turn descendent from Rhacdjcoe'a). 2. 

 Strongylaria (a) Echinocephala (^Echinodsia, ancestral 

 group, desicendent in turn from Gastrotricha) ; (b) Nema- 

 toda (with gordiids as most primitive forms because of 

 parenchyma); (c) Acanthocephala; (d) Chcietognatha. 

 3. Prosopygia ( = Molluscoidea) and 4. Frontonia (=Nem- 

 ertea). Rotatorian-like Trochozoa ancestors were as- 

 sumed for the Molluscoidea, Nemertea, and Echinodermata, 

 while annelids were derived from nemerteans. Arthro- 

 pods were derived biphyletically from the Chaetopoda in 

 two lines, — one the Crustacea, the other the Tracheata. 

 Chordates were derived from trochophore-'ike ancestors 

 in icommon with those which gave rise to the Nemertea. 

 Pentastomes and tardigrades were both incrluded in the 

 Annelida. 



Biitschli formed the group Nematorhyncha to incclude the 

 Gastrotricha and Echinodera (Atricha) ; he related 

 both of these groups to rotatorians on the basis that 

 the somatic musculature in all three groups does not 

 form a tube but consists of isolated cells extending 

 through the body cavity as in a Pilidium. He also con- 

 sidered these forms as close to the ancestors of arthro- 

 pods. Nematodes and nematorhynchs were closely as- 

 sociated with each other because of the superficial simi- 

 larity of echinoderids to gordiid larvae, the similarity of 

 the water vascular (excretory) systems of nematorhynchs 

 and nematodes, and the similarity of the mu5culature 

 of meromyarian nematodes to the musculature of gastro- 

 trichs. Complete absence of circular muscles wcis point- 

 ed out as the -chief factor separating rotatorian-nematcde- 

 nematorhynch series from annelid-gephyrean-platyhel- 

 minth series. The uniting of reproductive and digestive 

 systems in male nematodes, in both sexes in gjrdiids, 

 tardigrades and low arthropods he cited as evidence of 

 their common ancestry. The excretory systems of platy- 

 helminths, rotatorians, gastrotrichs and nemitodes were 

 considered undoubtedly homologous, while the tracheal 

 system of insects and the metamerically segmented or- 

 gans of annelids were considered divergent offshoots of 

 the same system. 



Stimulated by Gaffron's diagram of the nervous system 

 of an eetoparasitic trematode, Biitschli (1885) C3mpared it 

 with that of a nematode and judged therefrom that a 

 common ancestor must have existed. Th; d'^rsal brain 

 and lateral nerves of the trematode need only to have 

 bent ventrally forming a commissure in order ti form 

 a plan like that of a nematode. The later-il (amphidial) 

 by-pass (lateroventral commissure) of nematodes pre- 

 exists in trematodes. 



Zelinka (1896) supported the opinion that gastrotrichs 

 and rotatorians must have been derived fr^m a trncho- 

 phore ancestor and that echinoderids and nematodes 

 probably arose from gastrotrichs. 



Zacharias (1885) felt that he had established beyond 

 doubt the common ancestry of nematodes and rotatorians 

 on the basis of similar development (? bilateral c'eavage). 



Grobben (1910) crystallized the formation of a rota- 

 torian-nematode group naming it the Ascho'minthes and 

 differentiating it from the Platyhelminthes on the basis 

 of body cavity vs. parenchyma. In this 'j;rouD he in- 

 cluded Rotatoria, Gastrotricha, Echinodera, Nematoda, 

 Nematomorpha and Acanthocephala. 



Martini (1913) considered the possible relationship of 

 nematodes to both platyhelminths and arthopods and 

 concluded that nematodes by possessing a hind gut are 

 higher than platyhelminths, that the rectal glands of nema- 

 todes are homologues of tardigrade and insect malpighian 

 tubules and that the excretory system of neraas might 

 have had a separate origin and might not b? homologous 

 with thvit of platyhelminths. 



Steiner (1919, 1920) sub.scribed to the general -concept 

 of Biitschli (1876) but was more explicit in the com- 

 parison of organs in nematodes and rotatorians. In gen- 

 eral, it was his conception that nematodes developed 

 from organisms similar to the philodinid rotatorians. He 

 described the primitive nematode as a partially seden- 



192 



