ON ECHINORHYNCHUS ANTARCTICUS AND ITS ALLIES. 43 



neck,* in the shape and size of the embryos, and in the number of testes and relative 

 sizes of the sexes. With reference to E. piriformis, the shape comes nearest to that 

 of E. antarcticus, but the distribution of body-spines is different. They agree in the 

 absence of a neck region, and differ in the nature of the sub-cuticular canals and in the 

 number and rows of rostral hooks. Similar observations apply to E. striatus, and 

 all the points are characters of specific significance. 



The rostrum in E. antarcticus is larger in proportion to size of body than that of 

 the others, and the number of rows of hooks much greater. The size of the shelled 

 embryos also is distinctive. They range from '057 mm. to '19 mm. in length, and even 

 within the same animal considerable variation may be met with. DE MARVAL in- 

 variably speaks of the ova ("oeufs") as triple-shelled, but his figures are those of 

 embryos in which both ectoderm and endoderm are differentiated, and it is with these 

 that the embryos of E. antarcticus are compared in the foregoing table. 



* DE MABVAI thus distinguishes the neck and false neck : "Nous appelons 'cou' tout organs nettement deliraite 

 du corps, soil par un etranglement, soit par une ligne de demarcation bien nette, contenant totalement on en partie 

 seulement la poche qui vient s'inserer a son bord anterior. Le cou, non invaginable, supporte a son extremite le rostre, 

 qui, la plupart, du temps, semble ne former avec lui qu'un seul et nu-me organe. . . . Nous appellerons par centre ' faux 

 cou ' toute partie delimitee on non du corps, nue ou garnie de petits aiguillons, et n'dtant somme toute que le corps 

 proprement did effile en avant, ou la base du rostre tres allongee. Nous parlerons done, dans la suite, suivant le cas v 

 d'un cou et d'un faux cou, nus ou armes." 



EXPLANATION OF TEXT-FIGURES. 

 ?. = rostrum, f.n. = false neck. 



Figs. 1, 2, and 3 from DE MARVAL. 



Figs. 1, 3, and 4 are magnified about 10 times ; fig. 2 rather more. 



EXPLANATION OF PLATE. 



B. = Bursa. 

 Cut. = Cuticle. 



C.M. = Circular Musculature. 

 ECT. = Kctoderm. 



END. = Endoderm. 

 G.AP. = General Aperture. 

 P. = Penis. 



SC. = Sub-cuticle. 



Fig. 1. Female of Ecliinnrhijnrhus antarcticus, n. sp. x 10. 



Fig. 2. Types of rostral hooks in series. 



Fig. 3. (a) Tail of female, showing cleft. x 12. 



(b) Tail of male, with penis and bursa, extruded. x 12. 



Fig. 4. Surface view of body-wall as seen from inside, to show ramification of sub-cuticular canals, x 12. 



Fig. 5. Section of body-wall through spiny region. x 220. 



Fig. 6. Retractor muscles of rostral sheath. x 220. 



Fig. 7. Rostrum and portion of disc. x 30. 



Fig. 8. Triple-shelled embryo, x 220. 



(ROY. soc. OF EDIN. PROC., VOL. xxvi., PP. 445-446.) 



