266 SUMMARY OF CURRENT RESEARCHES RELATING TO 



associated in pairs. The paired association becomes more intimate in 

 telophase, giving rise to bivalent chromosomes in baploid number. A 

 brief diffuse stage (stage a) ensues in which the chromatin stains only 

 slightly. Then the double chromosomes reappear, apparently in the 

 same form and relative position as before, and condense into bivalent 

 prochromosome-like bodies (stage i). The ordinary leptotene condition 

 appears to be omitted entirely. The bivalent- bodies of stage b elongate 

 into diplotene threads that remain relatively condensed and clearly 

 separate throughout the entire growth period, giving rise to the bivalent 

 prophase chromosomes. In another species, A. notatus, the process 

 appears to be essentially the same, but is somewhat confused by a 

 spinning out and intertwining of the threads in the stage following 

 stage b. The usual synaptic process is entirely wanting in Asilus. 

 Synapsis is effected in telophase at the beginning of the growth period 

 by an intimate association of chromosomes that were already paired in 

 anaphase. Superficially the early growth stages resemble those of 

 Hemiptera and other forms, but the chromatic structures are bivalent 

 instead of univalent. Tetrad structures are not visible. The first 

 division appears to be reductional for all the chromosomes. J. A. T. 



Simulium Larva from Mountain Stream in Java. — A. L. J. 

 SuNiER {Natimrkund. Tijdschr. NederJand-LuUe, 1919, 73, 26-44, 

 2 pis. ; and ihid., 1920, 79, 205-20, 1 pi., 1 fig.). In a mountain 

 current of the Gunung Pangerango, in Java, at a level of about 

 1000 metres, numerous larvas of a species of SimuUiim were found 

 clinging to a submerged stone or moving against the current. There 

 are hooked clinging-organs anteriorly and posteriorly, and threads of 

 silk issue from the mouth. The anterior fan -like structures act as 

 strainers which catch microscopic particles, which are brushed by the 

 mouth-parts into the buccal cavity. The gut contained fine vegetable 

 detritus, diatoms, a piece of the ectocyst of a Bryozoon colony, and 

 minute remains of some small Arthropod. 



The larva presses its head against the substratum, secretes a silk- 

 loop, and fixes to this its anterior clinging-organ. The posterior 

 clinging-organ grips about the same p]ace, and then the anterior one 

 lets go. The newly-produced silk is colourless and transparent. The 

 clinging-organs are anchored exclusively to the silk-loops. In letting 

 loose its grip the posterior clinging-organ is invaginated. During this 

 process the rectal gills are completely retracted. They are protruded 

 again after the re-anchoring of the posterior clinging-organ. Then the 

 anterior organ is loosened and the body stretched forward. By alter- 

 nately fixing its gripping organs the larva can move against a very 

 strong current. The elaborate cocoon of netted silk-threads is described. 



J. A. T. 



Mutations in Drosophila.— H. J. Mijller (Journ. Exper. Zool., 

 1920, 31, 44o-73, 3 figs.). Discussion of three new mutations of the 

 gene W in the X chromosome of Drosophila melanogmter. They have 

 given rise respectively to : {a) Ecru, causing the eyes to be of a light 

 straw colour, not much darker than white ; {h) ivory, causing a light 

 yellow eye colour, only slightly darker than ecru ; and (c) white pro- 



