ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 55 



bution of Cladocera. The species increase rapidly in number from 

 February onwards, and reach a maximum in September. The number 

 is maintained in October, which is the time of the maximum sexual 

 -activity, but suddenly decreases thereafter. 



Reactions of Daphnia pulex to Light and Heat.* — R. M. Yerkes 

 finds that this water-flea is strongly positively phototactic to all inten- 

 sities from to 100 candle-power. There is no evidence of preference 

 for a certain intensity. The heat accompanying the light from a 

 16 candle-power incandescent lamp does not seem to have any influence 

 upon the direction or rate of movement. 



Heat in the absence of light has a directive influence upon the 

 movements ; the animal is negatively thermotactic at a temperature of 

 about 28° C. In a trough containing water of 28° C. at one end and 

 25° at the other, the animals migrated towards the region of lowest 

 temperature. The fact that in the case of Daphnia phototactic reactions 

 cannot be changed from positive to negative or the reverse by changes 

 in temperature, indicates that light does not act upon the organism in 

 the same way as heat does. 



Unpaired Eye and Frontal Organ of Branchiopods.f — N. von 



Zograf takes a comparative survey of the structure and development ol 

 these organs in various Branchiopods. The median eye, especially in 

 its central vesicle, is a very ancient structure with great uniformity of 

 development. The frontal organs are primitive retrogressive structures, 

 which probably formed originally a peripheral sensory apparatus. The 

 " Nackenorgan " has no phylogenetic significance : it is a typical gland, 

 probably assisting adhesion. Zograf concludes that the median eye and 

 the frontal organs were possessed by the Prot- Arthropods, and thence 

 transferred to Crustacea and Gigantostraca. 



New Pycnogonid from the South Polar Regions. J — T. V. Hodgson 

 ■describes Pentanymphon antarctic am g. et sp. n., secured by the ' Dis- 

 covery ' during her stay in winter-quarters in McMurdo Bay. It seems 

 to be fairly common. The only feature of importance which separates 

 it from the genus Nymphon is the presence of a fifth pair of legs, a 

 character which separates it from all Pycnogonids hitherto known. It 

 is noted that the Scottish Antarctic Expedition obtained several speci- 

 mens of a ten-legged Pycnogonid from the Weddell Sea, which may 

 prove to be identical with this species. 



Annulata. 



Tube-formation in Annelids. § — H. R, Linville, in an interesting 

 paper, gives an account of the habits of Ampliitrite ornata and Diopatra 

 cuprea, with especial reference to the formation of the tubes. The con- 

 sideration of minute adaptations of structure to function is the point of 

 the paper. 



* Mark Anniv. Vol.. 1903, pp. 359-77. 



t Das unpaare Auge, die Frontal organe und das Nackenorgan einiyer Bran- 

 chiopoden. 4ro. Berlin (1904) 44 pp., 3 pis. and 3 figs. See Zool. Zentralbl., xi. 

 (1904) pp. 729-34. % Ann. Nat. Hist., xiv. (1904) pp. 458-62 (1 pi.). 



§ Mark Anniv. Vol., 1903, pp. 225-35. 



