190 



SCIENCE. 



[N. S. Vol. XI. No. 266. 



colony or cell mosaic. DifFerentiatiou and cell 

 division, even in the spiral type of cleavage, 

 are independent phenomena, though they may 

 coincide more or less closely in point of time. 

 The spiral type must have been originally due 

 to mechanical causes, but is certainly, at pres- 

 ent, hereditary. It is followed by a bilateral 

 form of cleavage which is morphogenetio in 

 character, i. e., the direction and time of di- 

 vision and the size of the cells all contribute di- 

 rectly to the establishment of form in the 

 embryo. This bilateral cleavage has encroached 

 upon the preceding spiral period in consequence 

 of a condensation of the process of develop- 

 ment. The determinate character of the cleav- 

 age makes possible the massing of large amounts 

 of material in certain cells, which thus become 

 centers of distribution, but this segregation is 

 quantitative rather than qualitative so far as 

 ' organ forming material' is concerned. An 

 adequate conception of the extreme plasticity 

 of the cell is necessary for a satisfactory in- 

 terpretation of the phenomena of spiral cleav- 

 age. 



The second session of the Autumn Quarter 

 was held November 1st. Mr. R. H. Johnson 

 read a paper reviewing and criticising some of 

 the recent statistical literature upon the sub- 

 ject of variation. A second paper was con- 

 tributed by Mr. E. R. Downing reviewing the 

 experiments of Loeb, Morgan and others on 

 the production of cell division and development 

 in unfertilized eggs by chemical reagents. 



At the third session, November 15th, Mr. J. 

 M. Prather contributed the results of his study 

 upon the development of the hypophysis in 

 Amia. The hypophysis arises about one hun- 

 dred and sixty hours after fertilization, as a 

 local differentiation of hypoblastic cells in the 

 dorsal wall of the fore-gut far back of the point 

 of union of fore gut with stomodseum. Here 

 the base of the fore-brain is in very close con- 

 tact with the hypoblast, and this fact indicates 

 that its point of origin is determined by phys- 

 ical factors. Lobes begin to form about the 

 fifteenth day and by the thirty- fifth day the 

 organ is much lobed, chiefiy around the edges. 

 The first lumen appears near the center during 

 the ninth day, while others form in the lobes 

 as they arise. The lumina appear to have 



no communication with each other or with 

 the exterior. Neither blood-vessels nor nerves, 

 nor glandular secretions could be found in it at 

 the latest stage examined. The saccus vascu- 

 losus begins to form about the tenth day, as an 

 evagi nation at the posterior lower angle of the 

 infundibulum and grows backwards under the 

 base of the hind-brain. It is thus quite remote 

 from the hypophysis at all stages. Granular 

 secretions were found in it as early as the 

 twenty-second day. It is inferred that what 

 Kupffer considered the earliest stage of the hy- 

 pophysis in Acipenser is the anterior divertic- 

 ulum of the fore -gut which is naetamorphosed 

 into the adhesive organ. 



The second paper, read by Miss Anne Moore, 

 was an account of the morphology and life his- 

 tory of Dinophilua, D. Oardintri, found at 

 Woods HoU. Miss Moore succeeded in observ- 

 ing the actual encystment of DinophUus, thus 

 accounting for the sudden disappearance of the 

 animal noted by other authors. 



The fourth session, November 29th, was de- 

 voted to a paper by Mr. V. H. Lowe entitled, 

 ' Photographing Insects and other Animals.' 

 Mr. Lowe described in detail the apparatus and 

 methods employed in photographing animals in 

 the field and in the laboratory, including both 

 living and mounted specimens. The paper was 

 illustrated by a number of the author's lantern 

 slides. 



C. M. Child. 



OTTAWA riBLD-NATUEALISTS' CLUB. 



The third of the series of Winter Soir6es was 

 held in the Assembly Hall of the Y. M. C. A. 

 on January 9th. There was a good attend- 

 ance of members and strangers. Zoology, or- 

 nithology and geology formed the topics of 

 the evening. Professor E. E. Prince, B.A., 

 F.L.S., Commissioner of Fisheries for Canada 

 gave a most instructive paper ' On the Com- 

 parative Anatomy of the Ear,' in which he 

 traced the unity of arrangement in the struc- 

 ture and mechanism of that organ from the low- 

 est organism up to the highest, specially adapted 

 to receive vibrations and impart them to the 

 nerves connected therewith. By means of a 

 beautiful series of exquisitely prepared original 

 slides thrown upon the screen, Professor Prince 



