156 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
Doubling of Chromosomata in Nucleus of Selachian Ova.* * * § — Prof. 
J. Riickert, having investigated Pristiurus and Scyllium, comes to the 
conclusion that in the young ovarian ovum ( Eimutterzelle ) the chromatin 
framework is an enormously enlarged daughter-coil of the primitive 
ovum ( Urei ), whose chromosomata Lave been doubled and arranged in 
pairs. The doubling occurs in the transition from primitive ovum to 
young ovarian ovum, presumably by a peculiar longitudinal cleavage of 
the chromosomata in the dyaster stage of the last division of the 
primitive ovum. 
Hermaphroditism of Lampreys. f — Dr. J. Beard notes the occurrence 
of a well-marked ovum among the spermatozoa in the testis of a lamprey. 
Whether this condition is general in every male lamprey is not yet 
known. It is obviously of interest in connection with the hermaphro- 
ditism of Myxine (Cunningham, Nansen, Retzius), and the general 
problem of hermaphroditism. In reference to Myxine the author notes 
that the young forms have several rows of teeth along the roof of the 
mouth, a fact suggestive of some metamorphosis in the hag as well as in 
the lamprey. 
Theory of Mesoderm and Metamerism. :J — Prof. N. Cholodkowsky 
finds that the Metazoa may be distributed into three groups — Enterocoela, 
Genitocoela, and Acoela. To the first belong the Brachiopoda, Echino- 
derma, Chmtognatha, Chordata, and Enteropneusta. In the Genitocoela 
the coelom is said to arise in the compact mass of mesoderm, which 
corresponds to the sexual tissue of Platodes. It is not necessary to 
admit the existence in them of mesenchyme ; in some exceptional cases 
the gonads arise from special cells which are, as in Insects, differentiated 
before the formation of the germinal layers ; here are all Coelomata that 
are Enterocoela. The Acoela are the Coelentera, Porifera, Platodes, 
Nemertini, Orthonectida, and Dicyemida. 
The metamerism of the coelom of the Metazoa has a double origin 
and significance. In some animals (Enterocoela) it consists in the seg- 
mentation of various internal organs, and is due to the metameric 
ramifications of the intestine ■ in the Genitocoela it may be referred to 
linear budding. 
Metamerism of Vertebrates.§— Prof. B. Hatsehek corrects his pre- 
vious conclusion that the posterior nerve roots, which in Amphioxus and 
Ammoccetes are septal or inter-segmental, and the anterior roots, which 
are myal or segmental, so unite in higher Vertebrates in the spinal 
nerves, that a posterior root unites with the anterior root in front 
(rostrad), and that the ramus dorsalis ascending to the skin runs in the 
posterior (caudad) septum of the myotome. This is wrong. A posterior 
root unites in all higher Vertebrates with the subsequent (caudad) ante- 
rior root, and the branches follow the anterior myoseptum. He gives a 
table illustrating the relations which he believes to be correct. 
* Anat. Anzeig., viii. (1892) pp. 44-52 (2 figs.). 
f Tom. cit., pp. 59-60. 
X Congres Internat. Zoologie, II. i. (1892) pp. 58-65. 
§ Biol. Centralbl., viii. (1892) pp. 89-91. 
