• r >90 SUMMARY OF CURRENT RESEARCHES RELATING TO 



of the chromatin-nucleolus. They do not take part in the growth and 

 become small chromosomes. As such they appear in the spermatogonia 

 of the next generation. They go through the same modifications as the 

 regular large chromosomes, but pass undivided, as accessory chromo- 

 somes, into the spermatids. 



Inheritance of Dichromatism in Lina lapponica.* — Isabel 

 McCracken has made breeding experiments with this Chrysomelid beetle. 

 Her object was to observe through several generations the behaviour of 

 the particular differentiating character, colour, with the view of testing 

 for this insect Mendel's principles of dominance and segregation. Both 

 sexes are dichromatic ; they are easily distinguished by their size ; in- 

 dividuals may be mated for life, or males of one brood may be allowed 

 to mate freely with females of another ; life habits are adapted to 

 laboratory conditions, and at least five generations may be reared in a 

 single season. 



No amount of crossing between the two characters — melanic (B) and 

 brown dotted with black spots (S) — accomplishes any disintegration or 

 breaking-up of either one. In the offspring of a cross between the two 

 characters, either both characters, or only the spotted, may appear. 

 Cross-bred B's, namely B's appearing in a cross between the two 

 opposing characters, transmit B only to the offspring when similars are 

 bred together. Cross-bred S's transmit both opposing characters to the 

 offspring, these likewise transmitting both characters, though bred from 

 similar parents. In the third generation from similar parents, S's 

 appear to breed true. There is here no exact parallelism to Mendelian 

 results, but there are Mendelian features. The character S of S by B 

 parentage behaves like a dominant when mated with S. Character B 

 behaves like a Mendelian recessive in that from its first appearance it re- 

 produces B only. 



Bamboo-Beetle and Coffee-Plant.t — L. Boutan shows that a Xylo- 

 trechus, closely allied to X. quadrupes, which inhabits the dry bamboo- 

 stems, is a formidable enemy of the coffee-plant. The planters should, 

 therefore, carefully avoid the use of dry bamboos in their coffee planta- 

 tions, or should at least steep them in a solution of sulphate of iron. 



Sexual Dimorphism in Rat Louse.} — Giinther Enderlein describes 

 a striking instance of sexual dimorphism in Polyplax spi?iulosa of the 

 rat. The males have the normal number of tergites and sternites, while 

 in the females the tergites and sternites of the second to the seventh 

 abdominal segments (excepting the tergite of the third segment) are 

 divided into paired plates one behind the other. 



Reactions of the Pomace Fly.§ — F. W. Carpenter has experimented 

 with the common pomace or little fruit fly, Drossophila ampelophila 

 Loew. He finds, for instance, that the insect moves towards the source 

 of light, but when fatigued it seeks out the least illuminated spot and 



* Joum. Exp. Zool. ii. (1905) pp. 117-36 (1 pi. and 3 figs.). 



t Comptes Rendus, cxl. (1905) pp. 1654-6. 



t Zool. Anzeig., xxix. (1905) pp. 192-4 (4 figs.). 



§ Amer. Naturalist, xxxix. (1905) pp. 157-71. 



