946 SUMMARY OF OUKRENT RESEARCHES RELATING TO 



chanf»C8, Dr. I\I'Cook observed that spiders that live on plants as a rule 

 Lave colours that are harmonious with the prevailing greens and yellows. 

 Spiders that nest in stables, houses, on fences, &c., ordinarily have 

 dusky colours, harmonious with the environment. Ground spiders 

 generally have colours of neutral greys that blend well with the soil, 

 rocks, or stalks of grass, especially when the last are somewhat dry. 



On the whole, wo may conclude that many spiders that appear to be 

 more exposed to enemies by reason of bright colonre or greater size have 

 developed, or at least possess special variations in industry and habits 

 that in some degree are protective. But there are a number of apparent 

 exceptions which require more careful study before any general deduction 

 can be warranted. 



Development of Generative Organs in Araclmida.* — Herr V. 

 Faussek makes a welcome contribution to our scanty knowledge of the 

 development of the generative organs in Arachnida, in an investigation 

 based upon Phalamjium {cornutum ?). "When the segmentation of the 

 ventral plate begins, the rudiments of the reproductive organs lie as a 

 group of cells at the abdominal end of tlie embryo, protruding somewhat 

 into the segmentation cavity. The boundaries of the closely packed 

 cells are hardly distinguishable, the nuclei are large, the chromatin 

 granules isolated. 



When nerve-cord, &c,, are differentiated, the rudiment still lies as 

 before, inclosed in the mesoderm at the hind end of the nerve-cord. It 

 lies between the two mesoderm plates, in the future coelom. In the 

 liberated young, the rudiment is still an unpaired mass of cells, and soon 

 it becomes a differentiated organ. Only the female organ was traced. 



As to the origin of the germinal cells no quite certain answer can yet 

 be given. It seems very probable, however, that they arise directly from 

 the yolk-cells, contemporaneously with the appearance of the germinal 

 streak, and quite independent of the somatic cells of the blastoderm. If 

 this is so, it is interesting as another illustration of the very early 

 differentiation of the reproductive elements. 



Blood of Spiders-t — M. V. Wagner has investigated the blood of 

 spiders. It consists of a colourless liquid plasma in which float cor- 

 puscles or blood-cells. Blood freshly drawn from an adult spider 

 contains four kinds of cells, of whicb only two, the amoeboid and the 

 coloured, are constant. These two forms have some properties in 

 common, and have certain afiiuities of structure, but they differ widely in 

 regard to other properties, and in their mode of multiplication. They 

 also differ in origin, the former being mesodermic, the latter, endodermic. 

 The other two kinds of cells are only provisional stages of the constant 

 forms, and may be considered as the results of multiplication. The size 

 of the blood-cells increases with the age of the animal. In an adult the 

 proportion of the different forms of corpuscles, in the various regions of 

 the body, is strictly defined. During growth the proportion varies con- 

 stantly (in different stages), and periodically (in connection with the 

 skin-casting). The proportion is altered periodically by the sudden 

 appearance of the spherical forms whose number increases to excess 

 after the casting of the skin. As these spheres represent the stage of 

 multiidication in the constant forms, tliey indicate the intensity of the 



* Biol. Ceatralbl., viii. (1888) pp. 359-63. 

 t Arch. Slav. Biol., iv. (1888) pp. 297-336. 



