No. 3.] LOXOSOMA DA VENPORTI. 365 



reported up to this time which demonstrate that both sexual 

 conditions occur in the same animal at different times. 



The gonads are two nearly spherical masses of cells lying one 

 on either side of the median plane of the body in front of the 

 intestine and above the stomach (PI. XXXII, Fig. 4). Their 

 position is subject to modification by the contractions of the body 

 accompanying the closing of the lophophore. PI. XXXII, Fig. 2, 

 represents a section across a very strongly contracted animal 

 and shows the displacement of the gonads thus produced. 

 Here they are seen to lie one on either side of the stomach 

 and at some distance from the intestine. Each gonad, when 

 functional as an ovary (PI. XXXII, Figs. 4 and 13), consists of a 

 layer of smaller peripheral cells which surround a central space 

 occupied by one or occasionally two or three larger cells or ova. 

 The size of the ovary varies considerably, according to the 

 degree of maturity exhibited by the contained ova. Enclos- 

 ing the whole organ is a delicate structureless membrane. 

 PI. XXXII, Fig. 4, represents a section through an ovary con- 

 taining a nearly mature ovum. The cytoplasm is finely and 

 uniformly granular throughout, and appears to contain but a 

 small amount of deutoplasm evenly distributed. The germina- 

 tive vesicle is central, spherical, and has all of the chromatic 

 substance gathered into a single mass or nucleolus. This is 

 centrally placed and stains deeply with iron-haematoxylin. 



In the phase of activity when the gonads are functional as 

 spermaries, the whole mass is made up of many small, deeply 

 staining cells, as shown in PI. XXXII, Fig. 2. The cells of the 

 peripheral layer are smaller and less evident, and in sections can 

 be distinguished often around only a portion of the margin. 

 From the upper side of each gonad a narrow duct passes 

 upward and inward, just beneath the surface of the brain 

 (PI. XXXIII, Fig. 20), to the median plane, where it meets 

 its fellow from the opposite side. At the point of meeting a 

 swelling of the duct occurs, forming a little chamber, or sack, 

 which lies immediately below the brain commissure. From 

 it a short duct leads upward, to open in front of the commis- 

 ^re into the cavity of the atrium, just anterior to the intestine 

 (PI. XXXII, Fig. 4 ; PI. XXXIII, Figs. 22 and 23). In the 



