Anions' many representatives of the Spiruroidea and 

 Filarioidea the first stage larva bears hooks and spines 

 in the cephalic region. These same forms sometimes 

 have an attenuated tail (Gongylonema pulchrum, As- 

 earops strongylina, Physocephalus sexalatus and Dicheilo- 

 nema rhca). Both cephalic and caudal modifications are 

 lost at the first moult. Since this is the stage of entry 

 into the intermediate host these structures are probably 

 used for boring through the tissues of the host. The 

 occurrence of caudal specializations is characteristic of 

 certain species of spiruroids. In the Thelaziidae, the 

 tail is terminated by two or four small digitations in 

 Gongylonema pulchrum (Fig. 156 Z) while in Ascarops, 

 (15G CC) Spirocerca and Physocephalus (156 BB) it 

 takes the form of a round knob, said knob being unarmed 

 in Ascarops strongylina bearing a few spines in Spiro- 

 eerca lupi and many rounded protuberances in Physoce- 

 l>!>tilits sexalatus. According to Swales (1936) the tail of 

 the third stage larva of Tetrameres cravii (Fig. 156 R) 

 is abruptly truncate bearing a circle of nine digitations 

 of equal size and one subsequal median digitation; the 

 tail of Habroncma muscae has a rounded tip with many 

 smail spines while Seurocyrnea colini (Fig. 156 EE-FF) 

 has a similar tail but the knob is larger and the spines 

 relatively smaller. Cheilospirura hamulosa, of the Acuarii- 

 dae has a multi-pronged tail (Fig. 156 GG) in the third 

 stage while in the same stage Physaloptera turgida has 

 a bluntly conoid tail. 



In the Camallanoidea and Dracunculoidea (Fig. 156) 

 the first stage larva has a dorsal denticle (except 

 Micropleura) on the head, *and an attenuated tail with 

 large pocket-like phasmids. The dorsal denticle which is 

 lost at the first moult, might be considered homologous 

 to the hook present in the first stage Gongylonema. (Fig. 

 157 B-C). The tail of the third stage larva of Dracunculus 

 has four large mucrones while that of Catnallanus has 

 three prongs, the tail of the adults being conoid and 

 conkally rounded respectively. However in Procamallanus 

 fulvidraconis the three prongs persist to the adult. 



The posttmbryonic changes in the tail of Agamermis 

 decaudata Christie, (1936) are not limited to the cuticle. 

 The division between the anterior and posterior portions 

 of the body is marked by a node which is evident early 

 in the preparasitic larva. The posterior part, about 2/5 

 of the entire length, becomes detached at the time of the 

 entrance of the nema into the host. 



Hvpodekmis. The discussion of postembryonic develop- 

 ment in the hypodermis may be found on pp. 34-35 & 37. 

 Briefly, it may be noted that in the more generalized 

 nematodes little or no increase in number of cells or 

 nu:lei occurs after hatching while in moi'e highly evolved 

 forms many cell divisions or syncytial development may 

 occur. 



Teunissen (in Stekhoven, 1939) has found that the 

 number of hypodermal glands in young individuals of 

 Anaplectus granulosus is from 46 to 70 in a quadrant or 

 a total of 184 to 280. The number in juvenile males varies 

 from 204 to 312 while in young females they number 244 

 to 356. Before sex can be determined, young specimens 

 can be divided into two groups, those with 50 to 60 and 

 those with 60 to 70 glands per quadrant. Cells increase 

 in number as the nema grews, the number being con- 

 stant only in the adult. The number of glands in females 

 of 600 to 2000 microns length varies from 60 to 85 and 

 the number in the male of the same size varies from 

 50 to 75. One can be nearly certain that young specimens 

 with less than 55 hypodermal glands in a row will de- 

 velop into males and that those having more than 65 

 cells will develop into females. Cell constancy in the 

 individual is not reached until it is 1200 to 1400 microns 

 in length (or adult) since the number of hypodermal glands 

 is definitely larger in sexually mature specimens than 

 in larvae. 



Musculature, see p. 219. 



Nervous System. No changes known. 



Labial region and stoma. The labial region of most 

 nemas is not as distinctly set off from the remainder of 

 the body at the time of hatching as it is in the adult 

 stage, though there are some notable exceptions to this 



rule. Usually the cephalic papillae in parasitic nematodes 

 are relatively larger and better developed at the time 

 of hatching than in the adult. In rhabditids the labial 

 region is distinctly set off and the amphids are oval, 

 somewhat further posterior, and relatively larger than 

 in the adult stage (Fig. 158 W-Z). In strongylins three 

 or six indistinct lips are usually present in the first stage 

 larvae though lips may be totally absent in the adult 

 (Ancy lost oma caninum) . Furthermore, the cephalic papil- 

 lae show a much more generalized pattern at this time, 

 the internal circle and dorsodorsal and ventroventrai 

 papillae of the external circle being better developed than 

 in the adult stage in which these papillae are greatly 

 reduced. In ascaridids several changes take place in 

 the labial structures. Young ascaridid larvae, broken out 

 of the eggs have (Ascaris lumbricoides vide Alicata, 1935) 

 three small lips bearing the full component of separate 

 and well developed papillae (Fig. 158 J) while the 

 adult has large circumscribed lips with greatly reduced 

 and partially fused papillae (Fig. 57 Y, p. 60). What 



-esh 



*Moorthy. 1938, described a dorsal appendage on some specimens 

 of Dracunculus medinensis. In the first stage larva the appendage 

 is long and filiform ; while it persists throughout both second and 

 third stages it is greatly reduced in size disappearing entirely at 

 the third moult. 



Fig. 157. 



A-H — Developmental stages of Gongylonema pulchrum. (A — Fully 

 developed larva in egg ; B — First stage larvae, anterior end, lateral 

 view ; C — Same, ventral view ; D — Larva, four days after experi- 

 mental infection ; E — Same. tail, lateral view ; G — Second stage 

 larva, anterior end. lateral view ; H — Same, dorsal view ; I — Tail, 

 lateral viewi. J — Ascaris lumoricoides larva from egg, en face 

 K — Physocephalus sexalatus, third stage larva, en face. L — Gongy- 

 lonema pulchrum . posterior end, ventral view. After Alicata, 1935, 

 U. S. D. A. Tech. Bull. 489. 



229 



