OF THE COMMOX NEx^rATOUE OF THK DOGFISH. 453 



side. Linstow (9) has stated that the larger spicule is l:)ent into 

 a hook at its distal end, but I ha.ve not observed this arrange- 

 ment in any of the worms I have examined. It is covered with 

 numerous transverse markings, which give it a striated appear- 

 ance under a fair magnification, and attenuates to a point at its 

 distal end. Both spicules are ensheathed in cuticle. 



The "tail" of the male ends bluntly, and in the neighbourhood 

 of the spicules the cuticle is raised into rows of rounded eleva- 

 tions on the ventral surface. 



The tail of the female (text-fig. 3) is bent at an angle to the 

 body and is somewhat attenuated. In the region of the vulva 

 the cuticle increases considerably in thickness on the ventral 

 surface and forms a pad. 



Measurements in the case of Proleptus scillicola are almost 

 valueless, as there are wide variations not only in the sizes of 

 individuals, but also in the proportions of different parts. The 

 male varies considerably less than the female. 



Mature females vary in length fi-om 32* 17 mm. to 59 mni., and 

 the tail measures from '395 mm. to "583 mm. The proportion 

 of tail: total length varies from 1:75-47 to 1:146-6. Linstow 

 has given this proportion as 1 : 38-7. 



Tlie distance from the vulva to the tail-end varies from 

 •887 mm. to 1-06 mm., and the proportion of "Vulva to tail 

 end " : total length varies from 1 : 39-7 to 1 : 53-07. 



The males vary in length from 31-73 mm. to 36-2 mm. The 

 tail measures from 1-03 mm. to 1-56 mm., and the jn-oportion of 

 tail : total length extends between 1:19-66 and 1:30-8. Liu- 

 stow's proportion is given as 1 : 21-6. It would appeal- that 

 Linstow has based his proportion on mensurements of a single 

 A\'orm of each sex. 



(b) Internal Anatomy. 



The alimentary canal is normal, consisting of an resophagus, 

 intestine, and rectum. 



The (esophagus is of unequal thickness, being approximately 

 twice as broad behind the nerve-ring ns it is in front of it. In 

 the female it va,ries in length from 3-69 mm. to 5*86 mm., and 

 the proportion of oesophagus : total length varies from 1 :8-17 

 to 1 : 1 1 -52. In the male the cesophageal length fluctuates between 

 3-6 mm. and 4-53 mm., and the proportion of oesophagus : total 

 length from 1 : 7-32 to 1 : 8-81. 



In transverse section the lumen of the alimentary canal is tri- 

 radiate anteriorly, but towards the posterior poi'tion of the 

 intestine it becomes tetra-, penta-, or hexa-radiate. 



Rectal glands occur around the anterior end of the rectum in 

 both sexes. They are four in number and are symmetrically 

 arranged. 



The female reproductive system is typical, and the vulva opens 

 to the exterior, a short distance in front of the anus, on the 

 ventral surface. The eggs ai^e developed from a polynucleated 



