ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 45 



a discussion of the biological import of polar bodies, in which Zacharias 

 seems more inclined to side with Biitschli and with Weismann, than 

 with Minot or with Strasburger. 



IV. The act of Fertilization. — There are two pairs of conjugating 

 elements, male and female semi-mitoblasts. The result is two nuclear 

 structures mistaken for pronuclei, each consisting of a male and a female 

 semi-mitoblast. Hertwig's theory is entirely confirmed, though stated in 

 a new form. The whole point is that the union of sexual elements is 

 double, not single. 



V. The Segmentation. — A single segmentation nucleus is formed 

 eventually. The details of division are described. Zacharias confirms 

 Flemming's formula of repetition, according to which the daughter- 

 nuclei pass into rest by the star and coil stages, through which the 

 mother-nucleus passed out of it. The memoir, which is (unlike some 

 others of the kind) lucid and unambiguous throughout, closes with some 

 general notes on the relative importance of nucleus and protoplasm. 



Larval Stage of Species of Ascaris.* — M. A. Laboulbene, in oppo- 

 sition to the recently expressed views of Dr. Linstow, affirms that 

 Ascaris lumbricoides developes directly, or without the intermediation of 

 a second host. The ellipsoidal ova are evacuated before they have 

 undergone any segmentation ; the formation of the embryo takes about 

 thirty or forty days with a favourably high temperature, but may, as 

 Davaine has shown, be retarded for as long as five years with a low 

 temperature and a damp atmosphere. The embryo, as seen in the egg, 

 has an obtuse head, no lips, valves, or cephalic nodules ; its tail is 

 merely acute, and not filamentar. This embryo quits its egg-shell in the 

 stomach, or more often in the small intestine of the animal which it has 

 reached ; the shell is softened merely, and not dissolved by the gastro- 

 intestinal juice. The embryos now rapidly pass through a larval stage ; 

 twice only has the author seen it ; the first example was filiform, 

 20 • 4 mm. and ■ 5 mm. wide, and its head had three valvular and 

 nodulose projections ; the caudal extremity was truncated below, and no 

 genital organs were apparent. On the second occasion M. Laboulbene 

 found four examples, the exact dimensions of which were 2 mm., 

 3*25 mm., 1 cm., and 2*3 cm. He concludes that the development of 

 Ascaris lumbricoides is direct, the segmenting ovum giving rise in the 

 body of its definite host to the embryo, which rapidly reaches and soon 

 passes through the larval to reach its sexual condition. The experi- 

 ments of Grassi have shown that ripe ova may furnish sexual Ascarids 

 at the end of a month after swallowing. 



The ova of Ascarids, after passing with the faeces, are washed away 

 by rains, when they make their way into streams and ponds ; by watering 

 they are deposited on food-plants, and the evaporation of water allows 

 of their preservation in damp places. In the case of the dog the eggs 

 remain entangled in the hair, and the young, which lick their parents, 

 easily come into contact with them. The comparative rarity of this 

 human parasite in towns, and its frequency in rural places, is to be 

 explained by the fact that in the former the water generally is, and in 

 the latter is not filtered. 



* Comptes Kendus, civ. (1887) pp. 1593-5. 



