CHANGES IN THE SPLEEN OF THE FROG. 395 



These facts would lead us to expect better defined periodical 

 changes in the organs and tissues of temporaria than in those 

 of esciilenta. 



Cyclical Changes in the Organs and Tissues. 



Observations as to the cyclical changes in other organs than 

 the spleen will be mentioned here only in so far as they throw 

 some light on the changes in this organ. Ploetz in "Die 

 Vorgange in den Froschhoden unter dem Einfluss der Jahres- 

 zeit" states that the spermatozoa of R. temporaria are devel- 

 oped in the testes between the months of June and September. 

 The appearance of the spermatozoa in the testes remains the 

 same from September until the middle of March. From the 

 middle of March to the middle of April the spermatozoa pass 

 from the testes into the vesa afferentia. From the copulative 

 act until the end of May, such products as are not excreted are 

 reabsorbed. The testes of R. esadenta on the other 

 hand remain in nearly the same condition during the entire 

 year, always containing more or less developed sperma- 

 tozoa. 



It is probable from material collected, though not as yet 

 investigated, that there is an analogous difference in the de- 

 velopment of the sexual products of the female temporaria and 



esciilenta. 



In " Der Einfluss der Jahreszeiten auf die Leberzellen von 

 Rana temporaria;' I described the changed appearance in the 

 liver of male temporaria at different seasons. The varying 

 character of the blood vessels, the vacillating color and size 

 of the red blood corpuscles, the greater or less quantity of 

 pigment and the size and coloring of the liver cells and their 

 nuclei were the main points. 



Johannsen, in '' Ringbander der Nervenfaser," describes 

 some remarkable histological changes which take place in the 

 finest structure of the nerve fibers of R. eseidenta during -the 

 months of May and June. 



Gaule, in " Zahl und Vertheilung der markhaftigen Fasern 

 des Froschriickenmarks " says that the spinal cords of tem- 

 poraria are in their best condition in May, those of eseidenta 



