ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 47 



— a phenomenon to be compared with that observed by Delagc in the 

 case of Sacculina. 



In the case of the Monstrillid, a secondary process of development 

 begins as soon as the blood-vessel is reached, a cuticle is formed, and 

 two appendages appear in the form of unjointed tentacles, which are 

 bathed by the blood of the host, and constitute the organs of nutrition. 

 At the same time the cells of the body become differentiated into 

 layers. Later a pair of jointed antennae appear in front of the 

 " tentacles," showing that these are to be regarded as the second 

 anteniue. As at this stage the body is unsegmented, and appendages 

 homologous with mandibles are sometimes present, this must bo re- 

 garded as a second nauplius stage. From this point the development 

 takes place normally, save that that of the alimentary canal ceases with 

 the appearance of the stomodseum. Finally the adult leaves the body 

 of the host, and enters upon the brief free-living life. 



It is interesting to note that the eggs of the Monstrillid chiefly 

 studied — Eoemocera danse — are green, and, according to the author's 

 coloured plates, the same tint as the green blood of the Annelid host. 



Reaction of Daphnia to Light.* — C. B. Davenport and W. B. 

 Cannon have experimented on the effect of light on this crustacean. 

 They find that it moves, under certain conditions, from a strong light 

 to a feeble one, but this does not depend upon the intensity of the 

 illumination, but only upon its direction. In other words, Daphnia is 

 phototactic. A diminution of the intensity of the light only affects the 

 swiftness of the movements to a slight extent. Thus, when they 

 diminished the intensity to one-fourth the crustacean took 18 per cent, 

 more time to move over a given distance than when the light had the 

 original intensity. 



Spermatogenesis of Oniscus asellus.f — M. Louise Nichols finds that 

 in this form the spermatogonia chromosomes are joined together in pairs 

 in the synapsis to form sixteen bivalent chromosomes, and at this stage 

 a splitting of the chromosomes occurs. In the structure and mode of 

 origin of the bivalent chromosomes two main types may be distin- 

 guished, (1) that in which the component chromosomes lie end to end, 

 and (2) that in which they lie side by side. In the first maturation 

 division univalent chromosomes are separated, so that the division is 

 reducing. The idiozome is only discernible for a short time during the 

 prophases of the first spermatocyte. The nucleolus of the spermato- 

 gonium disappears shortly after the dissolution of the nuclear membrane, 

 while that of the spermatocyte first discovered in the synapsis persists 

 throughout the division. The spermatids become associated in groups 

 to form colonies of nuclei lying in a common plasma. Within the latter 

 arise bundles of fibres of great length, whose connection with the nuclei 

 could not be demonstrated, as well as single fibres of greater delicacy 

 which are continuous with the nuclei. The mature sperm colony con- 

 sists of a variable number of filamentous nuclei contained, together with 

 the bundle of cytoplasmic fibres, in a tenuous sheath, which is flagellate 

 at its anterior extremity. 



* Journ. Phvsiol., xxi. (1901). See also Bot. Ceutralbl., lxxxvii. (1901) p. 48G. 

 f Amur. Nat., xxxv. (1901) pp. 919-20 ;S tigs.). 



