228 Dr. W. H. Ransom on the Ovum of Osseous Fishes. [June 21, 



waves, which pass over the surface of the food-yelk, but also the fissile con- 

 tractility of the formative yelk, by virtue of which it cleaves into irregular 

 and unsym metrical masses, and which the author conceives to be regu- 

 lated only by the influence of the seminal particles. 



The cortical layer of the food-yelk or inner sac, which is shown to resist 

 in a remarkable manner osmosis, is found to be the rhythmically contractile 

 part, although requiring for its manifestation the presence of acid food- 

 yelk upon its inner surface. 



Evidence is given to show that the contractile property of the yelk of 

 both kinds requires, as an essential condition of its manifestation, the pre- 

 sence of oxygen in the surrounding medium, and that the food-yelk, while 

 the rhythmic waves are passing over it, consumes less than does the forma- 

 tive yelk, while regularly cleaving after fecundation ; also that some pro- 

 duct of oxidation is formed during these movements, which itself tends to 

 check them, but which the author failed to determine the nature of. 



Proofs are also given that a certain moderate rise of temperature in- 

 creases the activity of these contractions. Experiments are related which 

 show the extreme limits the yelk will bear without destroying them, and the 

 temperature at which commencing chemical change prevents further con- 

 traction. 



The reactions of the substance of the yelk under the stimulus of gal- 

 vanism are recorded, and evidence afforded that the food-yelk and the 

 cortical layer alone are excited to contraction by it, attempts made to in- 

 duce fissile or other contractions of the formative yelk resulting in elec- 

 trolysis of that highly unstable substance. 



Experiments made to ascertain the effects produced by poisonous sub- 

 stances on the contractions of the yelk are recorded, and the general fact 

 ascertained of the extreme indifference to such agents of yelk protoplasm. 



Carbonic acid, however, is shown to destroy the contractility rapidly, 

 and chloroform to arrest it for a time. 



The process of cleavage is described, and experiments are given which 

 show that oxygen in the surrounding medium is an essential condition of 

 its occurrence. The influence of heat in quickening it, and the comparative 

 indifference which it shows to the action of a galvanic current and to most 

 poisons, are proved by a series of experiments, in which also the remarkable 

 and destructive activity of carbonic acid is evidenced. 



The author has considered the egg as a cell, its contents as a pro- 

 toplasm, of which the firmer cortical* layer is the equivalent of the pri- 

 mordial utricle, and the fluid food-yelk of the liquid contents, while the 

 formative yelk is represented by the granular accumulation around the 

 nucleus. Two stages or grades of development of protoplasm are con- 

 ceived to be represented by the two forms of yelk, and a parallelism is 

 attempted to be drawn between them and the stages of development 

 through which many amoeboid organisms pass, and which the author 

 believes to have a wide, if not a universal existence in the organic world ; 



