546 SUMMARY OF CURRENT RESEARCHES RELATING TO 
tlie chromatin threads separate still more, become finer, and then dis- 
appear more or less completely. This is succeeded by a stage in which 
the chromatin threads form a diffuse framework of strands. Finally 
this concentrates into a coil. 
The fine distribution of the chromatin in the germinal vesicle during 
the growth of the ovum may be interpreted as an exaggeration of the 
normal nuclear activity. When the ovum ceases simply to grow, and 
exhibits specific functions of secretion, &c., the chromatin forms diffuse 
strands, perhaps securing the greatest possible surface for its opera- 
tions. 
The nucleoli are of import for individual life, not in connection with 
reproduction. Thus, during the intense differentiation of the large and 
complex ovum, the nucleoli increase greatly in size and number, and 
become apposed to the nuclear wall ; but when mitosis begins they dis- 
appear en masse. 
The first coil stage of the chromatin represents in these yolk-laden 
ova the first phase of mitosis — a palin genetic phenomenon. The diffuse 
threadwork is a csenogenetic adaptation. During the whole period of 
differentiation the coil-stage more or less persists ; after differentiation 
is over a thickening and concentration of the chromatin produces the 
secondary coil, which then enters into mitosis. 
Development of Teeth in Fishes.* — Dr. C. Eose finds that in Lepi- 
dosteus , the development of the teeth corresponds to the placoid type ; 
the epithelial tissue is the truly formative element ; no independently 
active growth of the connective-tissue papilla was to be seen. 
In young of Salmo salar , S. fario, Thymallus vulgaris , and Coregonus 
Hartmanni , the tooth-rudiments of the first series are all of the placoid 
type. But the first replacement teeth of Salmo salar are slightly differ- 
ent. A roundish epithelial knob, like a hair-rudiment, penetrates inwards, 
and only then surrounds the connective tissue papilla. This mode of 
development is intermediate between the placoid type and the occurrence 
of an epithelial dental ridge. 
Epiphysis of Teleostean Fishes and of Amia.j — Mr. C. Hill finds 
that, in various fishes, there are two epiphysial outgrowths from the roof of 
the primary fish-brain ; the anterior of these is considered to be homolo- 
gous with the parietal eye of Lacertilia, while the posterior is homologous 
with the epiphysis of those reptiles. It is probable that, in their 
primitive position, the two vesicles were side by side. It is thought 
likely that a study of the epiphyses of the larvm of Petromyzon w r ith 
special reference to their connection with the brain will yield results of 
great importance in settling the question whether the epiphyses were 
paired ancestral sense-organs. 
Development of the Kidneys in Anna calva. J — Dr. H. F. E. 
Jungersen found in the youngest embryo that the pronephric ducts 
showed no hint of tubules. Posteriorly, they united and opened behind 
the still closed anus ; anteriorly each exhibited two funnels opening 
into the abdominal cavity in the region of the pectoral fins. 
In the second stage, one ciliated funnel on each side opened into a 
* Anat. Anzeig., ix. (1894) pp. 653-62 (8 figs.), 
f Journ. Morphol., ix. (1894) pp. 237-66 (2 pis.), 
j Zool. Anzeig., xvii. (1894) pp. 246-52 (5 figs.). 
