Maech 25, 1910] 



SCIENCE 



463 



to occur in the development of Pennaria australis, 

 a hydroid having much in common with the local 

 species, and corroborating its phases of develop- 

 ment in a very remarkable degree. It may be 

 added that these facts taken with those already 

 known as to the perfect development of polyps 

 from even the most erratic early cleavage leave 

 no further room to doubt the perfectly normal 

 character of the phenomena described. 



Facts in the development of Glava, Eydractinia 

 and Tubularia were also cited as confirming the 

 previous conclusions, and thus further extending 

 the peculiar behavior under consideration. 



Associated with the above were certain infer- 

 ences and reflections of considerable theoretical 

 significance. Attention was directed especially to 

 facts of histogenesis. It was shown that much 

 of earlier speculation concerning this feature was 

 tinctured with error. Later facts of hydrozoan 

 ontogeny have not aflforded any clear support of 

 these earlier speculative contentions. Special em- 

 phasis was placed upon the fact that histogenesis 

 in ccelenterate ontogeny is of small homological 

 value and apparently wholly devoid of phylogen- 

 etic significance. In fact, the processes involved 

 in the formation of the germ layers are primarily 

 physiological and not morphological. Both ecto- 

 derm and entoderm arise thus; the first for pro- 

 tective and locomotor ends, the second for digestive 

 purposes and through specific digestive or nutri- 

 tive processes in the morula or planula. 



The detailed paper will appear later in the 

 Journal of Morphology, 



Development of the Paraphysis and Hypophysis in 

 the Alligator: A. M. Reese, West Virginia 

 University. (Presented by title.) 

 The paper will be published in full in the 



" Smithsonian Miscellaneous Collections." 



The Independent Origin and Self-differentiation of 

 the Lens of the Eye: Chakles R. Stockaed, 

 Cornell Medical School. 



Normally the embryonic optic vesicle comes in 

 contact with the lateral ectoderni of the head and 

 this ectoderm responds to the presence of the ves- 

 icle by proliferating a mass of cells which develop 

 into the crystalline lens. The question arises 

 whether the ectoderm may form a lens even though 

 the optic vesicle fails to come in contact with it, 

 and further, what influence does the optic vesicle 

 or cup exert over the subsequent development of 

 the lens? The problem is more complex than it 

 would seem at first sight and involves principles 

 similar to those expressed in the correlation be- 



tween the development of certain secondary parts 

 and the internal secretions formed by organs on 

 which these parts appear to depend. 



By artificially suppressing and retarding the 

 development of the optic vesicles in fish embryos 

 I have obtained exceptional material for the study 

 of the lens problem and from such embryos the 

 following conclusions may be drawn. 



A crystalline lens may originate from the ecto- 

 derm without any direct stimulus from either the 

 optic vesicle or the brain tissue. The independent 

 lens-bud is capable of perfect self-differentiation 

 and finally becomes a refractive body identically 

 similar in histological structure to a normal lens 

 within the eye. The size and shape of a lens are 

 not entirely controlled by the associated optic cup. 



An optic vesicle, whether normal or defective, 

 is invariably capable at some stage of its develop- 

 ment of stimulating the formation of a lens from 

 ectoderm with which it comes in contact. This 

 ectoderm may even be out of the usual lens-form- 

 ing region. Ectoderm of the head region, however, 

 is more disposed to the formation of lenses than 

 that of other parts of the body, as is indicated 

 by the fact that the free lenses invariably occurred 

 in this region. 



In Pundulus embryos the deeply buried optic 

 vesicles are unable to form lenses from their own 

 tissues, although this is not true in all animals. 



Further Data Gonoeming Twins: H. H. Wilder, 



Smith College. 



The distinction formerly made between the two 

 biological types of twins was reiterated, viz., 

 duplicates and fraternals, the one presumably 

 from the division of a single egg, after fertiliza- 

 tion; the other from two separate eggs. Outline 

 tracings of palms and soles of numerous individ- 

 uals were presented for examination and compari- 

 son. These showed (1) that in twins of the 

 duplicate type the main features in the configura- 

 tion of the palmar and plantar epidermic ridges 

 (friction ridges) are practically identical, and 

 always in the case of all four sets of members; 

 (2) that in twins of the fraternal type these 

 features are as unlike as in any two children of 

 one family but of different birth; and (3) that 

 although single hands or single feet, or perhaps 

 both hands or both feet, of two children of sepa- 

 rate birth, especially in a large family, might be 

 found to be as nearly alike as in cases of duplicate 

 twins, this similarity does not extend to all four 

 sets of chiridia, as always in these latter cases. 

 Tracings of four sets of duplicate twins, of four 



