48 FEBRUARY. 



these are developed into young animals, though their 

 united bulk ultimately equals that of the whole mass. 

 The greater number of these globules are not real eggs, 

 but only " yolk-spherules," destined to afford nutriment 

 to the true embryos, which greedily swallow them, 

 after certain changes have taken place, and increase 

 rapidly in bulk It is curious, however, that they do 

 not advance in development during this absorption of 

 nutriment, but are, so to speak, arrested until a great 

 augmentation of size is tlnis attained ; then they quickly 

 acquire the form of little free-swimming nautiloids, 

 closely like those of the Doris and Eolis, a form which 

 indeed is common to the early stages of all the known 

 higher mollusca, however various may be their adult 

 conditions. 



Here are the familiar Limpets, too : let us look at 

 them awhile. 1 They are not generally very attractive 

 in appearance, the shell being coarse and rubbed, 

 especially in the larger specimens ; and in an aquarium 

 they do not live long, and are so inert as to afford no 

 amusement even while they survive. Yet we occasion- 

 ally find examples prettily coloured ; and there are facts 

 in their economy which make them worthy of a few 

 moments' notice. 



1 Patella vulgata, represented by two examples in Plate v., at the left 

 side of the picture. 



