General Anatomy of Microfilaria. For a comprehensive 

 survey of the comparative anatomy of microfilarial spe- 

 cies the reader is referred to Puelleborn (1929). Regard- 

 less of the presence or absence of a sheath the embryo is 

 covered by a delicate cuticle with distinct but minute 

 striae (Rodenwaldt, 1908). The anterior end may bear 

 a delicate hook (Fig. 163 K) much like that of the first 

 stage larvae of spiruroids like Gongyloncma and filariids 

 like Dichcilonema. There is apparently no oral opening 

 and the stoma, at most, is indicated by a primordium or 

 vacuole. Paired "Mundgebilde" and "Schwanzgebilde" 

 have been demonstrated by intra vitam stains (Fig. 163 

 H-I) ; these seem to correspond to the amphids and phas- 

 mids. 



The remainder of the internal anatomy appears to 

 consist of a rather disorganized mass of cells or nuclei 

 some of which were sufficiently outstanding to have 

 received specific names. Manson (1903) named a clear 

 spot with a massive adjoining cell, situated in the 

 cervical region, the V spot. This was identified by Looss 

 (1914) as the excretory pore and excretory cell (Fig. 

 163 A & M). Rodenwaldt (1908) named four other 

 large densely staining cells Gl-4 considering them as 

 genital cells and the vesicle with which they are asso- 

 ciated, he termed GP or the genital pore. Looss considered 

 only the anterior-most of these (Gl) as a genital cell 

 and the remainder he named Zl-3 associating them with 

 the rectum and correctly identifying the vesicle as proc- 

 todeum. More recently Yamada (1927) and Feng (1936) 

 have found that all four G 'cells take part in the develop- 

 ment of the rectum (Fig. 164 5-9). Beneath the cuticle 

 there are four rows of spindle-shaped cells with elongate 

 nuclei which Rodenwaldt named the matrix cells of the 

 subcuticle. According to more recent observations, these 

 are somatic muscle cells and total 14 to 62 in various 

 species. The remaining nuclei of the body constitute the 

 nuclear column. These take part in the formation of 

 the esophagus, intestine, nervous system and chords. 

 In the cervical region they are particularly numerous, 

 interrupted only by the clear area indicative of the nerve 

 ring. In some species of microfilaria there is a clear 

 area beginning some distance posterior to the excretory 

 cell and ending anterior to Gl ; this structure, termed 

 the "Innenkorper" appears to be a yolk rest and corre- 

 sponds to the lumen of the future intestine (Fig. 163 A). 

 Near the tip of the tail, there is sometimes a pair of 

 tail nuclei which are lost at the first moult according 

 to Feng. 



Later development. For the later development of 

 microfilariae, we will use as an example M. malayi which 

 has been very nicely worked out by Feng (1936) as far 

 as the third stage (Fig. 164). In this species the sheath 

 is cast in the stomach of the mosquito on the first day. 

 Thereafter the organism is termed a first stage larva 



until the fourth day at which the first moult occurs in 

 the body of the mosquito. The second stage is terminated 

 ay a moult on the sixth day and the third stage continues 

 until after emergence from the intermediate host and 

 entry to the final host. During this period the nema 

 grows from a length of 210 microns and diameter of 

 4.8 microns to a length of 1.3 mm. and a diameter of 

 20 microns. Growth is not uniform; after entry into 

 the mosquito, there is first a shortening and widening, 

 chiefly in the mid-region, the minimum length occurring 

 after one and a half days (Fig. 164 7). On the second 

 day the mid-region starts to grow and after five and a 

 half days, the esophagus begins suddenly to increase 

 in length. The width increases up to five and a half 

 days, then diminishes. The tail of the first stage larva 

 is attenuated, that of the second stage short and conical 

 and that of the third stage truncate, with two ventral 

 and dorsal "papillae". (The ventral "papillae" are prob- 

 ably phasmids, while the dorsal is probably the tip of 

 the tail). In Dirofilaria immitis two massive protuberant 

 phasmids have been observed and no dorsal "papilla" 

 exists. The stoma begins to form on the second day. (Fig. 

 164 7) and by the fourth day (second stage) is indicated 

 by refractile rods (protorhabdions), (Fig. 164 9). In 

 the third stage the stoma is conoid and the head bears 

 the eight cephalic papillae and amphids characteristic 

 of adult filariids. 



The esophagus first becomes distinct (Fig. 164 8) on 

 the third day and takes the typical two part glandular 

 appearance of the adult by the fifth day. The intestinal 

 primordium is distinctly visible after 24 hours (Fig. 164 

 6) and is well formed on the third day (Fig. 164 8); by 

 the fifth day there is a distinct lumen and the intestine 

 is several cells in circumference. The rectal primordium, 

 Gl-4, begins with a division of Gl after 24 hours (Fig. 

 164 6) and a division of G2-4 accompanied by a second 

 division of Gl after 34 hours; the rectal cuticle completes 

 the formation of the 10 cell rectum on the third day 

 (Fig. 164 8). The genital primordium is first apparent 

 on the fifth day (Fig. 164 9) and is composed of seven 

 cells (Fig. 164 12); apparently it originates from cells 

 in the intestinal region but its earlier existence has not 

 been traced. In both the first and second ecdyses the 

 lining of the esophagus and rectum are moulted. 



Yamada (1927) had previously demonstrated two 

 moults after exsheathment for Wuchereria bancrofti while 

 the same number have been demonstrated in the inter- 

 mediate host of non-ensheathed microfilaria such as 

 Dirofilaria immitis. It seems clear that the ensheathed 

 microfilaria is an embryo rather than a larva. Even after 

 exsheathment the first stage larva is still rather embry- 

 onic in character and hardly deserves the term larva 

 tiefore the organs are demonstrable, this being on the 

 third day for Microfilaria malayi (Fig. 164 8). 



Bibliography 



Alicata, J. E. 1935. — The tail structure of the infective 

 Strongyloides larvae. J. Parasit., v. 21 (6) : 450-451, 

 1 fig. 



1935 (1936). — Early developmental stages of 

 nematodes occurring in swine. U. S. Dept. Agric. 

 Tech. Bull. 489, 96 pp., 30 figs. 



1937 (1938). — Larval development of the spiru- 

 rid nematode, Physaloptera turgida, in the cockroach, 

 Blatella germanica. Papers on Helminthology, 30 

 Year Jubileum, K. J. Skrjabin; pp. 11-14, figs. 1-13. 



Bovien, P. 1932. — On a new nematode, Scatonema wiilkcri, 

 gen. et sp. n. parasitic in the body cavity of Scatopse 

 fuscipes Meig. (Diptera nematocera) . Vidensk. Medd. 

 Dansk., Naturh. Foren., v. 94: 13-32, figs. 1-7. 



1937. — Some types of association between nema- 

 todes and insects. Vidensk. Medd. Dansk. Naturh. 

 Foren., v. 101: 1-114, figs. 1-31. 



Cameron, T. W. M. 1927. — Observations on the life 

 history of Aelurostrongylus abstmsus (Railliet), 

 the lungworm of the cat. J. Helminth., v. 5 (2) : 55- 

 66, figs. 1-2. 



Chitwood, B. G. and Wehr, E. E. 1934. — The value of 

 cephalic structures as characters in nematode class- 

 ification, with special reference to the superfamily 

 Spiruroidea. Ztschr. Parasit, v. 7 (3) : 273-335, figs: 

 1-20, 1 pi. 



Christie, J. R. 1934. — The nematode genera Hystrignathus 

 Leidy, Lepidonema Cobb and Artigasia, n. g. (Thelas- 

 tomatidae). Proc. Helm. Soc. Wash., v. 1 (2): 43-48, 

 figs. 15-17. 



1936. — Life history of Agamermis decaudata, a 

 nematode parasite of grasshoppers and other insects. 

 J. Agric. Res., v. 52 (3) : 161-198; figs. 1-20. 



1937. — Mermis subnigrescens, a nematode para- 

 site of grasshoppers. J. Agric. Res. v: 55 (5) : 353- 

 364, figs. 1-6. 



Cobb, N. A. 1890. — 0.ri/"?-i's-larvae hatched in the human 

 stomach under normal conditions. Proc. Linn. Soc. 

 N. S. Wales, 2. s., v. 5: 168-185, 1 pi. 



1925. — Rhabditis icosiensis. J. Parasit., v. 11 (4) : 

 219-220, figs. A-B. 



Cram, E. B. 1931. — Developmental stages of some nema- 

 todes of the (Spiruroidea parasitic in poultry and 

 game birds. U. S. Dept. Agric. Tech. Bull. No. 227, 

 27 pp., figs. 1-25, 1 pi. 



Crossman, L. 1933. — Preliminary observations on the life 

 history and morphology of Tylocephalus bacillivorns 

 n. g., n. sp., a nematode related to the genus Wilson- 

 ema. J. Parasit. v. 23: 106-107. 



Cuvillier, E. 1937. — The nematode, Ornithostrongylus 

 quadriradiatus, a parasite of the domesticated pigeon. 

 U. S. Dept. Agric. Tech. Bull. No. 569, 36 pp., figs. 1-6. 



?37 



