ZOOLOGY AND BOTANY, .MlCliOSCOPY, ETC. 333 



and connecting rhizoplasts, the primary giving rise to two fiagella, the 

 secondary to one and to the parastyle, the tertiary to the parabasal, the 

 peristomal fibril, and the cytostomal flagellnm or undulating membrane. 

 The centroblepharoplast complex is thus subdivided into four granules, 

 the centrosome and three blepharoplasts having continuous i-hizoplast 

 connexions with the central karyosome of the nucleus. The nucleus is 

 polarized with the centrosome anterior and the spireme forms in its 

 longitudinal axis. Binary fission in the cyst is morphologically longi- 

 tudinal. The blepharoplast-rhizoplast chain splits lengthwise at mitosis, 

 and the remainder of the neuromotor complex appears to be produced 

 de novo by outgrowths from the blepharoplasts prior to the spireme 

 stage. The .daughter centrosomes are connected by a paradesmose. In 

 mitosis the nuclear membrane remains intact and its constriction is 

 spatially transverse. The daughter nuclei are for a time connected by 

 the paradesmose, but lie at opposite poles of the cyst, but may later 

 change their position. The neuromotor system of CMlomastix is 

 strikingly similar to that of the right half of Giardia in symmetry and 

 in its constituent elements. The two daughter individuals are each 

 equivalent to the right half of Giardia. The bilateral symmetry of the 

 two-celled Giardia could arise only by a complete morphological reversal 

 from the sinistral to the dextral type of one of the two daughter 

 schizonts at mitosis. The genus Chilomastix is closely related in the 

 structure to the bilateral binucleate Hexamitid^ and may be their 

 source. J. A. T. 



Sensibility of Volvox to Light. — Henry Laueens and Henry D. 

 Hooker, Jun. {Jouni. Exper. Zool., 1920, 30, 345-68, 2 figs.). A 

 determination of the relative stimulating effect of radiation in different 

 parts of the spectrum. The sensibility of Yolvox to radiation of 

 different wave-lengths but of equal energy (sensibility to radiation at 

 equal energy) was investigated by two methods : (a) the relative 

 duration of the presentation time, and {b) the relative rate of locomotion 

 and precision of orientation. Both methods showed that a particular 

 wave-length has the highest stimulating value. The necessity of using 

 an equal-energy spectrum for such work is emphasized. J. A. T. 



Double Forms of an Amicronucleate Oxytricha. — J. A. Daw^son 

 {Joiirn. Exper. Zool, 1920, 30, 129-57, 22 figs.). In cultures of an 

 amicronucleate race of Oxytricha liymenostoma, under conditions similar 

 to those in which syngamy usually takes place in hypotrichous forms, 

 there is a strong tendency for the formation of double animals, or 

 "twins," by plastogamic dorsal fusion. Twins have all the structures 

 possessed by two single animals. They reproduce, giving {a) two pairs 

 of twins exactly similar to the parent ; {h) from the anterior portion, a 

 twin which pulls apart to form two single animals, and from the posterior 

 portion, a typical twin ; (c) from the anterior portion, two typical single 

 animals, and from the posterior portion, a typical twin. Twins may 

 form from normal strains, from descendants of single animals arising 

 from twins, and from the progeny of cannibal animals. In stock and 

 mass cultures they do not survive in competition with single individuals ;. 



