524 



SCIENCE. 



LN. S. Vol. XV. No. 379. 



(c) The third, from 10 mm. to about 80 

 or 100 mm. It is characterized by a num- 

 ber of changes which are positive as con- 

 trasted with degenerative. There are also 

 distinct degenerative processes taking 

 place during this ijeriod. 



(d) The fourth, 80-100 mm. to death. 

 It is characterized by degenerative pro- 

 cesses only. 



The eye of Amblyopsis appears at the 

 same stage of growth as in normal fishes 

 developing normal eyes. The eye grows 

 but little after its appearance. 



All the developmental processes are 

 retarded and some of them give out pre- 

 maturely. The most important, if the last, 

 is the cell division and the accompany- 

 ing growth that provide the material for 

 the eye. 



The lens appears at the normal time and 

 in the normal way, but its cells never 

 divide and never lose their embryonic char- 

 acter. 



The lens is first to show degenerative 

 steps and disappears entirely before the 

 fish is 10 mm. long. 



The optic nerve appears shortly before 

 the fish reaches 5 mm. It does not increase 

 in size with the gro-\vtli of the fish and dis- 

 appears in old age. 



The scleral cartilages appear when the 

 fish is 10 mm. long ; they grow very slowly, 

 possibly till old age. 



There is no constant ratio between the 

 extent and degree of ontogenic and phylo- 

 genic degeneration. 



The eye is approaching the vanishing 

 point through the route indicated by the 

 eye of Troglichthys. 



There being no causes operative or inhib- 

 itive, either within the fish or in the envi- 

 ronment, that are not also operative or 

 inhibitive in Chologaster agassizii which 

 lives in caves and develops well-formed 

 eyes, it is evident that the causes control- 

 ling the development are hereditarily estab- 



lished in the egg by an accumulation of 

 such degenerative changes as are still nota- 

 ble in the later history of the eye of the 

 adult. 



The foundations of the eye are normally 

 laid, but the superstructure, instead of con- 

 tinuing the plan mth additional material, 

 completes it out of the material provided 

 for the foundations. The development of 

 the foundation of the eye is phylogenic; 

 the stages beyond the foundations are 

 direct. 



Asymmetry in the Eattulidce, and the 

 Biological Significance of Asymmetry in 

 some Lower Organisms: H. S. Jen- 

 nings. 



The RattulidEe are a family of Rotifera 

 having an unsymmetrical form. The body 

 presents the appearance of having been 

 twisted, so that primitively dorsal struc- 

 tures are on the right side at the anterior 

 end, and on the left side at the posterior 

 end. An oblique ridge on the dorsal sur- 

 face passes from the rear forward and to 

 the right, ending frequently in one or two 

 teeth on the right side. It was shown that 

 this twisted form is an adaptation to the 

 method of life and behavior of the animals ; 

 they swim in a spiral, of which the twisted 

 body forms a segment, and the oblique 

 ridge marks the course of the spiral. The 

 reaction to stimuli is also correlated with 

 this form. It was further pointed out that 

 such an unsymmetrical form is common 

 among small organisms which swim in a 

 spiral course and react to stimuli in the 

 characteristic manner described in the 

 paper; this is true for example of most of 

 the free-swimming Infusoria. If radial 

 symmetry be considered characteristic of 

 a fixed life, bilateral symmetry of an 

 active life in which dorsal and ventral sur- 

 faces have different relations with the sub- 

 stratum, we may on similar grounds dis- 

 tinguish an unsymmetrical or spiral type. 



