ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 401 



Heterog^amy of Ascaris dactyluris.* — M. Mace describes the develop- 

 ment of Ascaris dactyluris, which live at the expense of the tissues of their 

 mother, till its body is reduced to a mere sac. The young are now well 

 advanced in development, the digestive apparatus being complete, and the 

 reproductive organs containing products which are apparently matured; 

 all these embryos are, without exception, females. The uterus is single and 

 not double as in the parent form. 



We have here a case comparable seemingly to that mode of development 

 of the larvsB of the Cecidomyige which has been called psedogenesis, but it 

 is to be noted that the reproductive individuals of these Nematoids appear 

 to be less advanced than the viviparous larvas of the Diptera. However, 

 the author has not been able to see these eggs undergo development, but he 

 believes that they escape to damp earth, and intends to investigate the 

 question ; if he proves to be correct in his supposition we shall have a case 

 similar to that of Ascaris nigrovenosa, where the female gives rise to herma- 

 phrodite ova ; or, in other words, we shall have among Nematoids another 

 instance of alternation of generations. 



Heterodera Sdiachtii.f — Herr A. Strubell finds that Reterodera is a 

 true Anguillulid, and stands nearest to Tylenchus ; the sexes are distin- 

 guished by a remarkable dimorphism, the male having the characteristic 

 nematoid form, and the adult female being spherical, and incapable of 

 movement. The cylindrical body of the male is from • 8-1 • 2 mm. long ; 

 the anterior part has a cap-like elevation which is separated from the rest 

 of the body by a circular groove ; the cuticle is distinctly ringed trans- 

 versely, the rings extending all round the body, and being only broken at 

 the lateral areas. The cephalic cap is to be regarded as the morphological 

 equivalent of the lips. The lateral areas are broad and are divided longi- 

 tudinally into three divisions ; there is only one excretory vessel. There 

 are four muscular areas, and in each there is seen, on transverse sections, 

 five muscle-cells ; the constituent elements are rather spindle-shaped than 

 rhomboidal, and the medullary mass exhibits no processes of any kind. In 

 Schneider's classification, therefore, Heterodera belongs to both the Poly- 

 myaria and the Platymyaria, and affords, therefore, a fresh proof of the 

 untenable character of Schneider's classification. No anal nerve-ganglion 

 could be made out. 



The spine in the buccal cavity is stilet-shaped and hollow, and has at its 

 base three knob-like thickenings ; it is moved by three pairs of muscles. 

 The last division of the oesophagus is chiefly distinguished by the presence 

 of remarkably large nuclei. When the spermatozoa are in movement 

 they emit extraordinarily long pseudopodia, which take on the most various 

 forms. 



The female of Heterodera has the form of a lemon with the poles drawn 

 out ; one of these processes is pretty sharply marked off from the chief 

 mass, and is seen to be the cephalic portion by the presence of a spine ; the 

 dorsal is always more strongly curved than the ventral surface ; the anus 

 lies near the vulva and dorsally. In place of the transverse annellation of 

 the cuticle there are five knobs and ridges which generally take a horizontal 

 direction ; the lateral areas cannot be detected from the exterior. The 

 genital apparatus consists of two tubes, which unite to form a common 

 vagina ; between the oviducal and uterine portions of each tube there is a 

 receptaculum seminis. 



The ovum is bean-, or kidney-shaped, and is inclosed in a firm structure- 

 less shell ; the yolk-elements are very large. Eggs at various stages of 



* ComptesHendus, ciii. (1887) pp. 306-8. t Zool. Anzeig., s. (1887) pp. 42-6,62-6. 



