Fig. 210.—Cephalic end of Dibothriocephalus cordatus; on the left viewed sideways, on the right from the dorsal surface, showing a suctorial groove. (After Leuckart.)
Length, 80 to 115 cm.; the head is heart-shaped and measures 2 by 2 mm. The suctorial grooves are on the flat surface; the segments commence close behind the head and increase rapidly in breadth. At only 3 cm. behind the head they are already mature; the greatest breadth attained by them averages 7 to 8 mm., the length 3 to 4 mm.; the number of proglottids averages 600; the most posterior ones are usually square. The uterine rosette is generally formed of six to eight lateral loops. The eggs are operculated and measure 75 µ by 50 µ.
Dibothriocephalus cordatus is a common parasite of the seal, the walrus and the dog in Greenland and Iceland, occasionally of man also. No doubt its larva lives in fishes.
The statement that D. cordatus also occurs in Dorpat in human beings has been proved erroneous (Zool. Anzeiger, 1882, v, p. 46), as also has the report that this worm lives in hares in the neighbourhood of Berlin, whither it was supposed to have been carried by Esquimaux dogs (Rosenkranz in Deutsch. med. Wochenschr., 1877, iii, p. 620). The parasite stated by the author to be D. cordatus is Tænia pectinata, Goeze, which has been known since 1766.
Dibothriocephalus parvus, Stephens, 1908.
Largest gravid segments 5 by 3 mm. Uterus forms a central rosette with four to five loops on each side of median line. In a proglottid measuring 3·5 by 2·25 mm. the genital atrium is situated 0·4 to 0·5 mm. behind the anterior margin and the uterine opening the same distance behind the genital atrium. Calcareous corpuscles absent in the preserved specimens. Eggs operculated, 59·2 µ by 40·7 µ.
Distinguished from Dibothriocephalus latus—(1) by the size of gravid segments (the minimum width of gravid segments of D. latus is 10 to 12 mm., so that D. parvus is a much smaller worm); (2) quadrate segments of D. latus measure 6 by 6 mm., those of D. parvus 4 by 4 mm.; (3) by the eggs.