REPRODUCTION AND GROWTH 263 



so far as can be judged from aquarium specimens. Dalyeli 

 kept a specimen of Actinia mesembryanthemum for sixty-six 

 years and specimens are still living which are known to be 

 almost as old. Orton {op. cit.) found that a specimen of 

 Sagartia viduata attained full size at a maximum age of 

 fourteen to fifteen months. 



Echinoderms. — The forms whose habits are of most 

 interest to us are the two starfishes Asterias mulleri and 

 Cribrella sanguinolenta. Both these forms, which occur 

 under stones in pools between tide-marks, carry their eggs 

 in pouches over the mouth, and hatch them there. Larval 

 starfishes are plentiful in summer and autumn. The 

 commonest form, Asterias rubens^ spawns in November at 

 St. Andrews, and may then be found grasping the ova in the 

 same curious stool-like position which is adopted when 

 devouring molluscs (M'Intosh, 1874, ^^^ see Plate XI). 



Annelida. — With few exceptions Polychaeta are uni- 

 sexual and oviparous. The common Nereis diver sicolor 

 has frequently been stated to be hermaphrodite, but 

 M'Intosh (1907) considers there is no foundation either 

 for this statement or for another which is frequently made 

 about this species, namely, that it is viviparous. Masses of 

 clayey mud, for instance, brought from the habitat of this 

 worm at St. Andrews showed many free ova. 



In the majority of cases the eggs are pelagic, but in others 

 they are demersal and surrounded by a layer of protective 

 jelly which is said to serve as food for the young larvae, e.g. 

 Aricia, Ophelia, Phyllodoce (Benham, 1896). In some Poly- 

 noids the eggs undergo part of their development attached 

 to the body of the parent beneath the scales or, in the case 

 of certain Syllids, attached to the ventral cirri. This tendency 

 towards a greater provision for the offspring is most pro- 

 nounced in Autolytus (Sacconereis) , where the eggs develop 

 within a ventrally-placed brood sac formed by the hardening 

 of a secretion. The young are liberated at an advanced 

 stage, being provided with head appendages and three pairs 

 of parapodia. As many as 300 embryos were counted in a 

 brood sac of Autolyttis ebiensis (Benham, loc. cit.). The eggs 



