200 M. E. CIai):uede on the Develupmeiit of Ncritiua fliiviatilis. 



fat-like substance. These glubules are enveloped by a thin, 

 colourless layer of a mucous matter, in which extremely fine 

 yelk-granules are imbedded. This is the food of the young 

 Neritina. The larva swims about in the water under the micro- 

 scope, and is soon seen to approach a yelk-mass and give it a 

 revolving motion by means of the cilia of the velum, whilst the 

 animal itself is stationary. l>y this means the globules aie 

 brought to the mouth, not to be swallowed at once, but merely 

 licked away. They are constantly turned before the mouth, 

 whilst the granules of the colourless outer layer are torn away 

 and swallowed by means of the cilia. They pass into the funnel- 

 shaped pharynx, where they are kept in tremulous movement by 

 the cilia, until they reach the abdominal cavity and unite with 

 the accumulation of nutritive material already existing there. 

 Although the yelk-granules of a globule are seen continually pass- 

 ing into the pharynx, their number does not perceptibly diminish ; 

 80 that one is compelled to suppose that new granules are formed, 

 probably from the transparent yelk-globule, to replace those 

 which are swallowed. This feeding of the young Neritince in 

 the capsule suffices to explain their great increase of size ; for 

 towards the end of its embryonal life the animals have attained 

 forty to sixty times their original volume. Carpenter states that 

 in Purpura this feeding can rarely be observed, and only under 

 peculiarly favourable circumstances; in Neritina it may be seea 

 with almost every embryo. The young animal sometunes swal- 

 lowed foreign bodies besides the yelk, when they came within 

 reach of the cilia of the velum : a Navicula or a Synedra was 

 several times carried into the pharynx. It must be remarked 

 that Koren and Danielssen represent the abdomen in young 

 embryos oi Purpura and Puccinuiii as filled with an aggregation 

 of yelk, consisting of uninjured eggs, although tlie oesojjhagus 

 is too narrow to allow of the passage of these. No eggs are 

 found in the abdominal cavity of embryos of Neritina in the 

 corresi)onding state, but merely an aggregation of larger or 

 smaller granules or drops, agreeing in nature and colour with 

 the vitelline substance. Nevertheless, the nutriment, when 

 swallowed, not very unfrequently cakes together within the em- 

 bryo in such a manner that similar formations might easily have 

 been mistaken by the Scandinavian naturalists for eggs. Their 

 statements with regard to the original aggregation and fusion 

 of the eggs for the formation of embryos, does not agree with 

 what takes place in Neritina; so that Carpenter has probably 

 come nearer to the truth. 



It is only after the embryo of Neritina has reached a certain 

 size, acquired a mouth and ocsoj)hagus, and eaten foreign yelk, 

 that the shell makes its appearance, and soon afterwards the 



