159. 



Postembryonic development of the reproductive system. A-J — 

 Turbatrix aceti [Diplogasteridae] (A — Genital primordium of newly 

 hatched female ; B — 24 hours ; C — Three days ; D — Five days ; E — 

 Ovary of nine day old female ; F — Genital primordium of newly 

 hatched male; G — Second day; H — Four days; I — Five days; J — 

 Testis). K-L — Syphacia obvelata, female reproductive system, im- 

 mature and adult. M-0 — Gongylonema scvtatum, genital primordium 



(M — Third stage larval female; N — Late third stage female; O — 

 Fourth stage). P-Q — Gaigeria pachyscelis genital primordium (P — 

 Fourth stage larval female ; Q — Late fourth stage female repro- 

 ductive system. 3 weeks old). A-J. after Pai, 192S. Ztschr. Wiss. 

 Zool.. v. 131 (2). K-L. after Vogel. 1925, Zool. Jahrb. Abt. Zool. 

 & Phys., v. 42. M-O, after Seurat, 1920. Hist. Nat. Nem. P-Q. after 

 Ortlepp. 1937. Onderstepoort J. Vet. Sci., V. S (1). 



interesting variations. The first stage larvae of Ascaris, 

 Toxocara and Toxascaris all have an esophagus which 

 s'ightly resembles that of rhabditids or more precisely An- 

 giostoma plelhodontis. It consists of a somewhat clavate 

 corpus, an indistinct isthmus, and a short pyriform bulbar 

 region. Information on the later development is lacking but 

 the adults have a cylindrical esophagus which in the case 

 cf Ascatis and Toxascaris is not grossly subdivisible into 

 separate regions. In the case of Toxocara the posterior 

 end is set off as a muscular ventricuhis, which apparently 

 corresponds to the reduced bulb of the first stage larva. 

 When an esophagael diverticulum is formed (Contracae- 

 eum), it develops as an evagination of the ventral side 

 of the bulbar region or ventriculus. The esophagi of 

 strongylins also pass through a very interesting series 

 of changes. In two superfamilies, the Strongyloidea and 

 Trichostrongyloidea the esophagus of the first stage 

 larva is usually identical with that of rhabditids (Fig. 

 158 A) ; during the second larval stage the valves de- 

 generate (Fig. 158 C) and in the third stage the esopha- 

 gus becomes long and narrow resembling the esophagus 

 of Diplogaster .except that the swelling at the base of the 



corpus is very indistinct (Fig. 158 D) ; in later develop- 

 ment it becomes more or less clavate, obliterating nearly 

 all signs of former division. Similar changes take place 

 in the Metastrongyloidea except that the phylogenetic 

 reminiscence of rhabditoid affinities is not so marked 

 since even the esophagus of the first stage larva does 

 not have a valvulated bulb but resembles more closely 

 that of third stage larvae of strongyloids and metastrong- 

 yloids. Two families of the Rhabditoidea, the Rhabdiasidae 

 and the Strongyloididae, undergo change in the form of 

 the esophagus during development of the parasitic genera- 

 tion. In the first family the esophagus of the free-living 

 generation and of the first stage of the parasitic genera- 

 tion is rhabditiform while the later stages of development 

 of the parasitic generation show changes entirely com- 

 parable to the strongyloids. In the second family the 

 esophagus of the free-living generation and of the first 

 stage larvae of the parasitic generation is rhabditiphani- 

 form while in the later development of the parasitic 

 generation changes comparable to those of rhabdiasids 

 occur except that the esophagus of the adult remains much 



232 



