NO. 1123. 



PROCEEDINGS OF THE NATIONAL MUSEUM. 



807 



Dimension of Octobothrium dipsacum. 



Measiirt-uieiits. 



Length 



Length of bothrium 



Length of contractile bulbs 



Diameter of contractile bulbH 



Length of proboscis (approximate) . . . . . 

 Diameter of proboscis, exclusive of hooks 

 Diameter of proboscis, including hooks . . . 

 Length of longest hooks 



The proboscides were not seen fully extended, but so far as unrolled 



tliey were clavate. 



The bothria were four, in pairs. Each bothriuui is provided on its 

 posterior edge with a small cup-shaped organ, about 0.01 mm. in diam- 

 eter which is eversible. When slight pressure was applied, these 

 organs were everted, when they appeared as small tubercles covered 

 with exceedingly fine, short, stiff-looking bristles, about 0.002 mm. in 



length. 



Behind the contractile bulbs, at the posterior end of the embryo, is 

 a short papillary projection, covered with very line downy bristles. 



The neck of the living embryo is translucent, and has the following 

 characters in optical section: There is first an outer granular layer 

 002 mm. thick, next a layer of transverse fibers 0.07 thick, next a 

 layer of longitudinal fibers 0.025 thick. Within is a central space 

 filled with a granular parenchyma containing numerous refractile 

 bodies In this central space also the branching and anastomosing 

 vessels of the water vascular system and the proboscis sheaths with 

 their retractile muscles can be made out. 



The arrangement of the hooks on the proboscides is characteristic 

 (figs 2 3) in that each has a longitudinal line toward which the shorter 

 diagon'al rows of hooks converge on each side, ^^ear the base of the 

 proboscides, where the hooks are somewhat scattering, from six to ten 

 hooks to a row could be counted on each side of the horizontal hue, 

 under favorable circumstances. More than twice that number could 

 be counted in the rows nearer the apex of the proboscis. 



13. Genus TETRARHYNCHUS. 

 (Plate VI, figs. (^-10.) 



I group together under this head a number of larv^ne from a variety 

 of hosts, some of which undoubtedly belong to this genus, but which 

 I am unable to identify certainly with any adult form; others may not 

 belong to the genus at all, notably numbers 7 to 11. 



1 Small cysts from serous coat of stomach of the dusky shark {tar- 

 charUnus obscurus) (No. 5480, U.S.N.M.), twice in August, 1884, and 

 again, July 25, 1887, Woods Holl, Massachusetts. 



