720 ON THE SPAT^-N AND YOUNG OP A FOLY0H.T5TE WOEM. [Dec, 17. 



whatever it be, which makes it undesirable for so many other 

 Eunicid larvae to pass through a pelagic stage, is at work here 

 also ; only that, instead of the early development being accom- 

 plished in the spawn-jelly, as in group ii., or in the body-cavity 

 of the mother, as in Marphysa sangidnea, the larvae make use of 

 the power, which they share with those of various other Poly- 

 ch^tes, of secreting mucus in quantities from their epidermal 

 glands, to attain the same end of providing a fixed resting-place 

 during the formation of the more important organs of the body. 



Btbliogbaphy. 



(1) Claparicde (E.) und E. Metschnikoep. — " Beitriige zur 



Kenntnis der Entwicklungsgeschichte der Polvchaten." 

 Zeit. f. wiss, Zool. xix. (1869). 



(2) Fewkes (J. W.). — " On the Development of certain "Worm- 



Larva?.'" Bull. Mus. Comp. Zool. Harvard, xi. (1885). 



(3) Haecker (V.). — "Pelagische Polychatenlarveu." Zeit. f. 



wiss. Zool. Ixii. (1897). 



(4) Koch (H.). — " Einige Worte zurEntwickelungsgeschichte von 



Eunice." Neue Denkschr, Allg. sehweiz. Gres. Naturw. 

 viii. (1846). 



(5) Keohn (A.) und A. Schneider. — " Ueber Annelidlarven mit 



porosen Hiillen." Arch. f. Anat. 1867. 



(6) MtJLLER (J.). — "Ueber die Jugendzustiiude einigerSeethiere." 



Monatsber. Akad. Berlin, 1851. 



(7) Salensky (W.). — " Etudes surle developpement des Anne- 



lides," deuxieme partie. Arch. Biol. vi. (1887). 



(8) Webster (H. E.). — " On the Annelida Chgetopoda of the 



Virginian Coast." Trans. Albany Inst. ix. (1879). 



(9) Wilson (E. B.). — "Preliminary Abstract of Observations 



upon the Earlv Stages of some Polychsetous Annelides." 

 Zool. Anz. iii. (1880). 

 (10) Wilson (E. B.). — " Observations on the Early Developmental 

 Stages of some Polychaetous Annelides." Stud. Biol. Lab. 

 Job. Hopk. Univ. ii. (1882). 



EXPLANATION OF PLATE XXXIX. 



Spawn and young of a Polycha'^te Worm of the genus Marpliym. 

 Fig. 1. Spawn-mass, unbroken, somewliat reduced, p. 715. 



2. Spawn-mass, broken, showing embryos and pellicle, somewhat 



reduced, p. 715. 

 o. Embryo in striated coat, greatly enlarged. The outline of the 



ectoderm underlying the coat is not shown, p. 716. 

 4. Young, stage 2, greatly enlarged, p. 716. 

 6. „ „ 3, ,, ■ „ p. 716. 



6. „ „ 4, „ „ p. 717. 



7. „ „ 6, „ „ p. 717. 



8. ,. „ 7, „ „ p. 717. 



9. „ „ 8, „ „ p. 718. 

 10. „ „ 11, „ „ p. 718. 



10 «. Jaws of stage 11, more highly magnified, p. 719. 

 10 ft. Setfc „ „ „ p. 719. 



The figures, which are copies of working drawings of the living objects, are 

 not drawn to scale ; but nos. 4-10 are yery roughly so. 



