NOTES ON HISTOLOGY OF LINGULA ANATINA. 25 



Yellowish brown pigment granules are found scattered here 

 and there along the supporting substance of the ileo-parietal band 

 and among the ova. They are compact and polygonal granules 

 of various sizes (PL IL, Figs. 27, 30). These granules must 

 have been formed by a process of pigment degeneration of the 

 young ova (early arrested in their development) and even of the 

 ripe ova. In large specimens of Lingida collected at the end 

 of the summer or in the fall, the ovary is found very much 

 reduced in size as dirty brown masses with black spots. On 

 cutting such an ovary into sections we meet with diverse stages 

 of karyolysis and plasmolysis of the ova ; the latter at first 

 provided with vesicular nuclei come to increase in consistency and 

 break up into granules. But I could not determine whether 

 it is only the ova left behind after the ripe ova had been 

 deposited that are subjected to degeneration or whether losing 

 the opportunity of discharging, the entire ovary, with both ripe 

 and unripe ova, turns into pigment granules. Must probably 

 both these things take place. Lankester ('73) found in Tere- 

 bratula vitrea the yellow matter among the ovarian ova and this 

 he considered as the envelope of escaped ova (p. 93). Joubin 

 ('86) states that on keeping Crania the eggs atrophied and turned 

 into brown bands (p. 255). 



b. Testis. 



In male individuals the spermatozoa are formed only in the 

 region corresponding to that in which the ova are produced in 

 the female. About the supporting substance of the ileo-parietal 

 band is a tolerably thick layer of cells with vesicular nuclei ; 

 this layer consists of the spermatogonia and spermatocytes. Ex- 



