360 Messrs. Koren and Danielssen on the 



the same time that we observe these, we see the traces of the 

 two pedal ganglia, which are placed side by side, more or less 

 oblong, and of a deep yellow colour. 



The margin of the mantle extending upon the dorsal surface 

 of the animal forms a cavity clothed with cilia, in which the 

 heart and the branchia? are placed. The first traces of the bran- 

 chiae were two scarcely visible cords, which, originating from the 

 margin of the mantle, met below, and formed an interlacement. 

 When the development was further advanced, we saw that these 

 cords were tubes which formed several loops, and that by this 

 means they had some resemblance to a corkscrew. The loops 

 were smaller above and below, whilst in the middle they were 

 broader and closer together. A brisk movement, produced by 

 cilia, was soon observed on their inner margins. In his memoir 

 Loven* has stated, that as regards the development there exists 

 a great resemblance between the Gasteropoda and the Acephala. 

 In the latter he has shown how the branchise are formed, and 

 we have had the opportunity of observing that this formation 

 takes place in the same way in Buccinum undatum and Purpura 

 lapillus. 



Nearly at the same time that the formation of the branchise 

 takes place, there appears at the bottom of the branchial cavity 

 a vesicle which is formed by the secretion of a greyish and semi- 

 transparent mass. Muscular fibres soon make their appearance 

 in this mass. The vesicle is oval and nearly pyriform, and ter- 

 minates below in a pretty long canal, which follows the course 

 of the intestine, but loses itself in the dark vitelline mass. We 

 could not observe any communication between the canal and 

 the heart, as was observed by Gegenbaur in the Pteropoda. 

 When the development is further advanced, the latter divides 

 into two chambers, of which one is smaller than the other. 

 Between these chambers there is a valve, which is always in mo- 

 tion. The walls of the vesicle are delicate, semitransparent, and 

 furnished with a multitude of muscular and varicose tubes, which 

 run in all directions, longitudinally and transversely. These tubes 

 are smaller than those in the heart ; for this reason a higher power 

 is necessary to observe them well. The contractions of the ve- 

 sicle coincide with the dilatations of the heart (and vice versa), 

 although it is impossible to perceive any communication between 

 these organs. It is filled with a clear fluid, in which a great 

 many dark molecules are found. We think that this organ is a 

 commencement of the kidney. 



Some time now passes without the appearance of other organs, 

 and everything seems to cooperate in completing all that has 



* Bidrag till Kannedomen om Utvecklingen af MoUusca Acephala La- 

 jnellibranchiata, p. 96. 



