Figure 45. Development of echinus, Echinus liwidus (by Krohn) . 



A — larva shortly after hatching: a — blunt pole; b — sharp pole; 

 c, c — cover; d — central cavity; e — accumulation of "nucleus- 

 like formations" from which the fibrous tissue is later 

 formed. 



B — "ideal sketch" of the larva, already having the form of the 

 body with three surfaces: a, b, c — anterior, posterior, and 

 upper surfaces; d — anterior angle; e, e — posterior angles; 

 f — lower angle ; g — anus . 



C— — cross-section of this same stage of development, in which 

 for elucidation of the passage the previous apple-shaped 

 form was drawn: a, b, c, d, e, f, g — as in figure B; 

 h — rudiment of the digestive tract in immature form; 

 k — its rudiment in later form. 



D — larva of the following form, back view: a, b — posterior and 

 upper surfaces; c — anus (back passage) ; gg, 11, kk — rudiments 

 of club-shaped, arch-shaped, and transverse branches of 

 calcareous skeleton. 



E — later larva: a, b : c, g, k, 1 — as in figure D; dd — rudiment 

 of posterior limbs; hh — first traces of hydrants in it. 



F — larva of pear-shaped form, back view: dd — posterior limbs; 

 ee — anterior limbs; f— -mouth; q — -anus; ssss — cilia apparatus. 



G — calcareous skeleton of the formed larva, represented in 



an isolated view: gg — club-shaped hydrants; hh — hydrants of 

 anterior limbs; kk — arch-shaped hydrants; 11 — transverse 

 hydrants . 



579 



