forming a covering for the germinal cells and a terminal 

 cell (Fig. 159 G). After 96 hours, no change had taken 

 place except multiplication of cells (Fig. 159 H) but after 

 120 hours the anterior somacic cells had grown posteriorly 

 drawing the anterior part of the gonad with them (Fig. 

 159 I). Thus the flexure of the testis takes place. Finally 

 the anterior somatic cells grow posteriorly and join the 

 rectum forming the vas deferens and cloaca (Fig. 159 J). 

 Alicata (1935) found the development of the male re- 

 productive system of Hyostrongylus rubidus to be essen- 

 tially similar except that multiplication of germinal cells 

 (P5) is delayed. As in Turbatrix, the anterior group of 

 somatic cells (S5 I) bend posteriorly forming the vas 

 deferens and seminal vesicle but the germinal zone is 

 shifted around so that it is anterior and the gonad con- 

 sequently is not flexed (Fig. 162). Goodey (1930) en 

 the contrary found that in Tylenchinema oscinellde the 

 posterior terminal cell group extends posteriorly forming 

 the vas deferens and joining with the rectum.. In this 

 species the testis is not flexed. 



Microfilaria and Filarial Development. Work on 

 microfilaria has been developed as a separate science with 

 little or no relationship to general Hematology. Since 

 the pioneers were chiefly interested in identification of 

 forms found in the blood of various species they developed 

 a separate nomenclature for parts of the 'body. Recent 

 workers have made rapid strides in the identification of 

 the parts of microfilaria with other nematodes'. 



Some filarioids give birth to well formed first stage 

 larvae or deposit well formed eggs containing such 

 lo.rvae. These were placed in the family Filariidae by 

 Wehr (1935). The larvae of such forms often have the 

 cephalic hook and transverse rows of spines as seen in 

 Gongylonema pulehrwm (Fig. 157 B) ; some of these 

 have attenuated tails, others rounded and spinate tails 

 as in Gongylonema. They are moderately well differen- 

 tiated first stage larvae and in many cases, at least, 

 should not be called microfilaria. This term should he 

 reserved for the rather unformed or embryonic young- 

 produced by the genera placed by Wehr in the Filarii- 

 dae. In these, stoma, esophagus, intestine and other 

 organs are not completely differentiated. 



Microfilaria may be classified as to presence or absence 

 of a sheath (Fig. 163 J-K). The sheath is a very delicate 

 membrane surrounding the larva, which some authors 

 have considered a cuticle, indicative of the first moult, 

 eth?rs a modified egg shell. The fact that the sheath 

 insists chemicals in which a vitelline membrane would 

 be dissolved, eliminates that possibility. Evidence that 

 tVe sheath develops from an egg membrane was presented 

 hv Penel (1904) and Seurat (1917) in the cases of 

 Lou, loa and Thamugadia hyalina (Fig. 163 B-G). Its 

 insolubility in alcohol and oils would signify that if it is 

 an egg membrane, it is the shell. There seems to be no 

 morphologic difference correlated with presence and ab- 

 sence of a sheath. 



Fig. 163. 



Postembryonic development continued. A, H-I, and M — Microfilaria 

 loa (A — Entire larva; H — Tail showing [ihasmids ; 1 1 1 . ;i <l ; M — 

 Excretory pore and cell). B-G — Thamugadia hyalina, successive 

 stages. J. — Microfilaria bancrofti, head. K-L — Mf. recondita, head. 

 lateral and ventral views. N — Heterodera schachtii, fourth stage 



male in preparation for moult. O-Q — Capillaria colitnibae. 

 A, H-M, after Fuelleborn. 1929, Handbuchen Path. Micro, v. 6 (28). 

 B-G. after Seurat. 1920, Hist. Nat. Nem. N, after Strubell, 1S88. 

 Biblio. Zool. Orgi. Abh. Gesannnt. Zool.. v. 2. O-Q, after Wehr, 

 L939, l T . S. D. A. Tech. Bull. 673. 



236 



