being reduced thereafter. Alicata (1935) records eight 

 dorsal and eight ventral intestinal cells in both first and 

 third stage larvae of Hyostrongylus rubidus. The present 

 writer found seven dorsal and seven ventral cells in the 

 intestine of the first stage larvae of Trichostrongylus 

 axei, 22 cells in the second stage and only 16 in the 

 intestine of the infective third stage larvae. The writer 

 makes no attempt to explain the reduction in number of 

 cells but the data were verified with numerous specimens. 

 Nuclear division without cell wall formation must occur 

 later in the development of strongylins (Fig. 102, p. 102). 

 In the case of mermithoids our information is more 

 definite. In many of these species cell division is followed 

 by nuclear division without cell wall formation and finally 

 fusion of syncytia and obliteration of the lumen may occur. 



Outpocketings or cecae have been previously described 

 (p. 100) in diverse groups of nematodes. In ascaridins 

 such cecae have been found to arise as evaginations of 

 the intestinal epithelium during late larval development. 

 Similarly, Christie (1936) has found that the trophosome 

 (the fat body or intestine) of mermithids grows anteriorly 

 during larval development of Agam.erm.ts decaudata. On 

 this basis we may consider the trophosome in the esopha- 

 geal region of mermithids as a caecum without a lumen. 



Rectum, Cloaca and Pertaining Structures. In so far 

 as is known, cell division does not take place in the 

 postembryonic development of the posterior gut of the 

 female. It does, however, in the male for a small ventral 

 growth of cells forms which is later joined by the vas 

 deferens when it comes to open in the cloaca. Similarly, 

 there is a mass (or two masses) of cells from which 

 the spicules develop. The gubernaculum, on the other 

 hand, is a cuticular thickening of the dorsal lining of the 

 cloaca. One may interpret the spicular sheaths as first 

 an evagination of the dorsal wall of the cloaca, then an 

 invagination of this structure (Fig. 118 U). Both spicules 

 and gubernaculum generally develop during the fourth 

 stage. 



Excretory System. Conclusive evidence is lacking with 

 regard to the postembryonic development of the excretory 

 system despite the numerous observations which have been 

 made. The primary cause of this failure is that all workers 

 have proceeded on the assumption that a single ventral 

 gland cell is the entire system. Cobb (1890) described 

 the excretory system of larval Enterobius vermicularis 

 as a single invaginated cell from which the lateral canals 

 and excretory vesicle developed. In 1925 the same author 

 described the first stage larva of Rhabditis icosiensis as 

 similar to that of the adult except that the ventral gland 

 was unpaired and the lateral canals free in the body 

 cavity; the unpaired ventral cell was then supposed to 

 divide forming the double glands of the adult. The sinus 

 and terminal duct nuclei were not accounted for. Stek- 

 hoven (1927), Lucker (1935) and others have described 

 a sinus (no nucleus seen) two subventral gland cells 

 and no lateral canals in third stage larvae of the 

 strongyloids. The writer found the excretory pore, 

 terminal duct, sinus, subventral gland cells and lateral 

 canals all very plain in the first stage larva of Tricho- 

 strongylus axei (Fig. 158 A-B). Before theorizing too 

 much on the development of the excretory system, it 

 would seem necessary that more critical data be obtained 

 on the actual conditions existent in first stage larvae. 

 It seems possible that the so-called ventral gland or 

 excretory cell usually described in larvae of parasitic 

 nemas is actually the sinus cell and the terminal duct 

 cell may be present but overlooked. If this is the case, 

 the system may originate from two germ lines in the 

 Phasmidia. The primary sinus nucleus might easily give 

 rise to a secondary sinus nucleus and the paired subven- 

 tral glands of the Strongylina and some rhabditids (R. 

 icosiensis, R. terricola, R. strongyloides) . This would still 

 not account for the lateral canals. The theory that they 

 develop from the sinus cell may be correct but it has 

 not been demonstrated. 



Fig. 161. 



Postembryonic development of female reproductive system of 

 Hyostrongylus rubidus, with position of coelomocyte adjoining genital 

 primordium. A — First stage ; B — third stage ; C — Preparasitic third 

 stage larva. D — Third stage larva recovered 2 days after experi- 

 mental infection. E-H — Third stage 4 days after experimental in- 

 fection. I — 5 days after experimental infection, larva on verge 

 of third moult. J — Vulvar region showing differentiation of ovary 

 and gonoduct at 9 days. L — Female larva after 9 days. M — Young 

 adult female, posterior end. All after Alicata, 1935, U. S. D. A. 

 Tech. Bull. 489. 



Female Reproductive System. Development of the fe- 

 male reproductive system may be of two types, dependent 

 upon the number of ovaries present in the adult. In 

 either instance the genital primordium of the first stage 

 larvae consists of the same number of cells, four, arranged 

 in the same manner as in the males. Tnrbatrix aceti is 

 the only one ovaried form that has been studied. Pai 

 (1928) found that after 24 hours the posterior somatic 

 cell group (S5 II) has multiplied considerably, forming 

 a mass of cells while the other cell groups (S5 I and P5) 

 remained constant (Fig. 159 B). Later all cell groups 

 multiply (Fig. 159 C-D) and the anterior end of the 

 gonad bends posteriad while the posterior end (S5 II) 

 grows posteriad also (Fig. 159 E). The anterior somatic 

 cell group forms the epithelium of the ovary while the 

 posterior somatic cell group forms the oviduct, uterus, 

 and seminal receptacle. At this time an invagination of 

 the hypodermis of the ventral chord meets the uterus 

 forming the vagina and vulva. 



The gonad of Tylenchinema oscinellae was found by 

 Goodey (1930) to develop in the same manner except 

 that a twist occurs in the oviduct. The vagina and 

 uterus of Sphaerularia and Atractonema were found by 

 Leuckart (1887) to become everted or prolapsed grov/ing 

 until the uterus is hundreds of times larger than the body 

 in Sphaerularia (Fig. 115A). 



The development of the female reproductive system 

 in nematodes with two ovaries {Falcaustra lambdiensis, 

 Gaiaeria pachyscelis and Hyostrongylus rubidus) differs 

 in that both of the somatic cells form ovarian epithelium 

 and both contribute to the formation of the uterus. Divi- 

 sion of the terminal cells results in an epithelial tissue 

 covering the germinal cells with a terminal cell at the 

 end of each ovary and a mass of somatic cells separating 

 the two groups of cells resulting from the divisions of 

 P5 I and P5 II (Fig. 161). This mass of cells through 

 further division and enlargement pushes the germinal 

 cell groups apart and finally forms the uterus and ovi- 

 ducts. At this time the middle part of the S5 group is 

 joined to an invagination of the hypodermis forming the 

 vulva and vagina, (Fig. 161 J). Ortlepp (1937) found 

 that the ovejectors of Gaigeria pachyscelis (Fig. 159 

 P-Q) originate from the genital primordium and not 

 the vulvar invagination. Free-living nematodes with out- 

 stretched ovaries undergo no further development unless 

 parts of the uteri are set off as seminal receptacles. 

 Free-living nematodes with opposed reflexed ovaries differ 

 only in that the ends of the ovaries grow towards each 

 other. Seurat (1920) found that in the case of parallel 

 ovaries or uteri in parasitic nematodes that the ovaries 

 and uteri are at first outstretched; coiling and twisting 

 of ovaries, uteri or both occur in very late larval or early 

 adult development. Another peculiarity in parasitic nema- 

 todes is that the uteri may become fused for part of 

 their length forming either a continuation of the vagina 

 (vagina uterina) or a common uterus. The transforma- 

 tion from opposed to parallel oviducts and coincident 

 development of a long uterine vagina was particularly 

 well illustrated by Vogel (1925) in the development of 

 Syphacia obvelata (Fig. 159 K-L). 



Male reproductive system. The genital primordium 

 of the male nematode consists of four cells at the time 

 of hatching in all known cases. Two of these cells, the 

 "terminal cells" cover the other two, the germinal cells. 

 Unfortunately the development has been traced only in 

 nemas having a single testis in the adult. Seurat (1918) 

 discovered that the anterior end of the gonad of Falcaustra 

 lambdiensis first grows anteriad, thereafter turning post- 

 eriad and extending to the cloaca, thus forming the vas 

 deferens with the result that the gonad is flexed. 



Pai (1928) found that in Turbatrix aceti after 48 hours 

 the genital primordium consisted of three groups of cells 

 the primordial germ cells (P5), the anterior somatic 

 cells (S5 I) forming a solid mass derived from the anterior 

 terminal cell, and the posterior somatic cells (S5 II) 



Fig. 162. 



Postembryonic development of male reproductive system of 

 Hyostrongylus rubidus. Al — First stage larva. Bl — Later first 

 stage larva. CI — Late first stage larva. Dl-El — Second stage larva. 

 Fl — Preparasitic larva. Gl — 2 days after experimental infection. 

 Hl-Jl — 4 days after experimental infection. Kl — 5 days after 

 infection. LI — 6 days after. MINI — Fourth stage larva 9 and 11 

 days after. 01 — 11 days. PI — Young adult male, posterior end. 

 All after Alicata. 1935, U. S. D. A. Tech. Bull. 489. 



235 



