TORN ARIA 123 



which the form of the adult can be more or less 

 clearly discerned, unless, as in the case of the 

 above-named starfish, the adult form has suffered 

 a peculiar change from a bilaterally symmetrical 

 type. 



The general name of the pelagic larval form 

 of those Enteropneusta (Balanoglossida), which 

 produce small ova not exceeding 0.15 mm. in 

 diameter, is Tornaria. All members of the 

 families Ptychoderidae and Glandicipitidae (or 

 Spengelidse) produce such eggs, The Harri- 

 manidae produce large yolky eggs from 0.4 mm. 

 in Dolichoglossus kowalevskii to as much as 

 1.5 mm. in Stereobalanus kupfferi. Tornaria 

 was discovered in 1848 by the famous German 

 physiologist Johannes Miiller of Berlin, who 

 thought that it was an Echinoderm larva ; its 

 real nature was determined in 1869 by Professor 

 Elias Metschnikoff. 



It is well known how much the quantity of 

 food-yolk in the egg-cell affects the course not 

 only of the segmentation-stages, but also of the 

 subsequent embryonic and larval development; 

 and that, under normal conditions of nutrition, 

 the size of the egg is a fairly constant specific 

 character. 



The dimensions of the eggs of different animals 

 do not always vary in proportion to the bulk of 

 the progenitors. Amongst existing birds, where 

 oviparity is the rule without any exceptions, the 



