442 On the Development of the Pectinihranchiata. 



d, branchial ganglion ; e, intestinal ganglion ; /, the two small 

 pedal ganglia; g, commissures of the small cerebral ganglia 

 to the pedal ganglia ; h, commissures of the large cerebral gan- 

 glia to the branchial ganghon ; i, commissures of the large pedal 

 ganglia to the branchial ganglion ; k, auditory nerves ; I, optic 

 nerves ; m, nerves (commissures) of the large pedal ganglia to 

 the small pedal ganglia; n, nerves which arise from the large 

 pedal ganglia, and ramify; o, nerves of the small pedal ganglia, 

 which also ramify ; p^ nerve of the intestinal ganglion ; q, nerve 

 of the heart ; r, nerves of the intestines. 



Magnified about 150 diameters. 



Fig. 2. An embryo of Purpura lapillus recently detached from the common 

 mass of eggs : a, conglomerated eggs ; b, membrane furnished 

 with cilia ; e, the commencement of the rotatory organs, furnished 

 with cirrhi. 



Fig. 3. An embryo seen from the back : a, b, c, as in the preceding figure ; 

 d, the foot further developed and furnished with cilia. 



Fig. 4. An embryo seen from the back : a, c &c d, as in the preceding ; 

 b, the shell; e, salivary glands; /, tentacles; g, eyes; h, heart; 

 i, mantle. 



The following Figures are magnified about 200 diameters. 



Fig. 5. An egg of Buccinum undatum in which the vitellus has divided into 

 numerous spheres of segmentation : a, membrane ; b, spheres of 

 segmentation. 



Fig. 6. An embryo formed by a single egg, of which the vitellus has 

 divided into two spheres of segmentation : a, exuded mass ; 



b, two spheres of segmentation. 



Fig. 7. An embryo also formed by a single egg, in which some organs are 

 already formed : a, membranous shell ; b, mantle ; c, two spheres 

 of segmentation ; d, rotatory organs ; e, foot. 



Fig. 8. The embryo of one egg, seen from the ventral surface, and in the 

 centre of which four spheres of segmentation are seen : a, mem- 

 branous shell; b, mantle; c, four spheres of segmentation; 



d, rotatory organ ; e, foot, with auditory organs. 



Fig. 9. An embryo with eight equal spheres of segmentation : a, mem- 

 brane ; b, spheres of segmentation. 

 Fig. 10. The same embryo a little more advanced in development. 

 Fi^s. 11, 12. The same embryo, more advanced: «, shell; 6, mantle; 



c, spheres of segmentation ; d, rotatory organs ; e, foot. 



Fig. 13. An embryo seen from the ventral surface : a, membranous shell ; 

 b, mantle; c, spheres of segmentation; d, rotatory organs; 



e, salivary glands ; f, oesophagus ; g, pharynx. 



Fig. 14. An embryo seen from the back : a, b, as in fig. 13 ; c, rotatory 

 organs ; d, foot ; e, salivary glands ; /, stomach ; g, pharynx. 



Fig. 15. An embryo formed of three eggs, seen from the back : a, b, as 

 in fig. 13; c, vitelline mass; d, e, as in fig. 13; /, foot; 

 g, pharynx. 



Fig. 16. An embryo seen from the back : a—/, as in preceding; g, sto- 

 mach ; h, oesophagus. 



Fig. 17. An embryo formed by three eggs : a — g, as in fig. 16 ; A, pharynx ; 

 », heart. 



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