Development of the Pectinibranchiata. 441 



vesicle^ and that it occurs deeper in the branchial cavity. This 

 is also an error on the part of l)r. Carpenter; it is himself, again, 

 that is deceived ; and we can affirm this without fear, as by our 

 frequently- repeated observations we have confirmed our first im- 

 pressions. And when, in conclusion, Dr. Carpenter asserts that 

 we have also made several mistakes in the ulterior development, 

 we are led to believe, from all that we have just explained, that 

 Dr. Carpenter has no right to reproach us therewith. But before 

 concludmg these remarks, we should state that our observations 

 on Buccinum ttndaturn and Purpura lapillus no longer stand 

 alone; for, without taking into account that M. Leuckart has 

 made diff'erent observations equivalent to ours in the article 

 " Zeugung," in ' Wagner's Handworterbuch der Physiologic,' 

 M. Lindstrom has shown, in the ' Ofversigt af Konglige Veten- 

 skabs-Akademiens Forhandlingar 1855,' that the embryo oi Ne- 

 ritina fluviatilis, Linn., is developed in a similar manner to that 

 of Buccinum undatum and Purpjura lapillus. The egg-capsules 

 contain 30-40 eggs, from which only a single individual is de- 

 veloped. 



EXPLANATION OF PLATES XVL and XVII. 



[The figures here given are only a selection from those of the authors.} 

 Plate XVI. Magnified about 150 diameters. 



Fig. I . Grouped eggs and newly-formed erabrj'os of Buccinum undatum, the 

 greater j)art of which are already furnished n ith rotatory organs, 

 foot, auditory organs, salivary glands, and heart : a, the mass 

 exuded from the eggs; b, the softened chorion; c Sc d, mem- 

 brane surrounding the eggs ; e, an embryo formed by a single egg. 



Fig- 2. An embryo seen from the ventral surface : a, membranous shell ; 

 b, mantle ; c, eggs ; d, heart ; e, rotatory organs ; f, foot ; g, au- 

 ditory organs ; h, salivary glands ; i, pharynx ; k, oesophagus ; 

 /, stomach; m, brancbiaj. 



Fig. 3. An embryo seen from the side : a, shell ; b, eggs ; c, foot ; d, rota- 

 tory organs ; e, tentacles with eyes ; /, heart ; g, the large 

 cerebral ganglia ; h, the small cerebral ganglia ; i, commissures 

 of the pedal ganglia ; k, auditory organs ; I, commissures of the 

 branchial ganglion ; in, branchial ganglion ; n, nerves of the 

 intestines ; o, pedal ganglia ; p, salivary gland ; q, branchia ; 

 r, retractor muscle ; s, stomach ; t, intestine ; u, liver, and above 

 this the contractile vesicle (kidney). 



Fig. 4. An embrjo seen from the side: a, shell; b, siphon; c, foot; 

 d, operculum ; e, tentacles. 



Plate XVII. 



Fig. 1. Nervous system of an embryo, somewhat compressed, magnified 

 about 200 diameters : a, the two large cerebral ganglia; b, the 

 two small cerebral ganglia; c, the two large pedal ganglia; 



