Introduction to A nimal Morphology. 



most in Holothuria?. The fibres are usually unstriped, 

 except in the jaw-muscles of Echinus, and the longi- 

 tudinal bands in Synapta. A non-ciliated, pseudhsc- 

 mal circulatory system exists in most species, consist- 

 ing of a ring-like (arterial r) canal, between the nervous 

 and water-vascular rings around the oesophagus, 

 with sometimes a second circum-anal (venous :) circle, 

 and a fusiform muscular heart, uniting the two 

 circles. 



The sexes are separate (except in Synapta, 

 Molpadia, &c.) The eggs are small, consisting of a 

 shell, albumen, and a fine-grained yelk; development 

 begins by the disappearance of the germinal vesicle, 

 and may be direct, but usually the egg produces a 

 larva (pseudembryo, [f. Thomson}, of which (except 

 in Crinoids and Holothurians) only the part around 

 the digestive canal develops into the mature form, 

 the rest being only provisional. This larva is 

 bilaterally symmetrical, and resembles that of some 

 <<f the Annulosa. In this 



^e all Echinoderms arc 

 ^omcwhat like in struc- 

 ture. From the egg is 

 emitted a ciliated planula, 

 whose cilia become re- 

 stricted to transvcr.su or 



ral bands, which often 

 eloi into proces 



A stomach and intestine 

 form within, bi-^innintr 

 I>o;; '.wards, 



iing at first by an 



, ... I'll:' 



anus,but soon developing ::ioillh- 



Fig, [9, 



I 



