ON SOME PLY.MOUTH HOLOTHURIANS. 



217 



out by further investigation. The usual number of gonadial tubes in 

 C. saxicola may therefore be fairly stated as 24 or 25. Curiously enough, 

 about 25 is also the average number of tubes given for the whole of the 

 50 specimens examined. There is variation, however, in the number 

 of gonadial tubes in this species between 10 and 61, as has already been 

 observed. 



It is an interesting fact that the males appear to be more variable in 

 this respect than the females, although the small number of individuals 

 examined necessitates caution in making this suggestion. Of the 50 

 specimens examined 24 were females and 26 males. The number of 

 gonadial tubes in individual females varied between 10 and 33, whilst 

 in the males the variation lay between 15 and 61. The total number of 

 gonadial tubes in all the females was 477, giving an average of less 

 than 20, while all the males gave a total of 769, giving an average of 

 about 29-5. 



10-15 16-20 21-25 2(3-30 31-35 36-JO 41-i5 46-50 51-55 56-60 

 Numbers of gonadial tubes. 



Fig. 3. — Curve showing the frequencies of different numbers of the gonadial tubes in 

 50 specimens of Cucumaria saxicola B. and R. 



Ordinates = frequencies ; abscissae = number of gonadial tubes between 

 10 and 15, 16 and 20, and so on. The continuous line denotes the actual curve 

 obtained, the dotted one an ajiproximation to the form of the curve if a larger 

 number of individuals were examined. 



THE GONAD OF CUCUMARIA NORMANI. 



The gonad of C. normani consists of a very large number of small 

 cylindrical tubes of almost even bore. These tubes are arranged as in 

 C. saxicola, on each side of the mesentery supporting the alimentary 

 canal. The tubes on both sides open into one longitudinal collecting 

 duct which extends in the mesentery some distance behind and in front 

 of a point about the middle of the length of the body. This duct is 



