SEA-FISHERIES LABORATORY. 



355 



layer of cells beneath the outer dead layer. Eventually 

 a thin layer of chitin is secreted on the outer side of these 

 cells (Text fig. 9, E.), and this layer of chitin is continuous 

 with the exoskeleton. The old membrane, which is now 

 almost black, becomes worn oif, and this new chitinous 

 membrane is exposed. 



The cells in the new layer of epidermis become 

 extremely active, and increase in number internally. At 

 first an undifferentiated mass of cells is formed beneath 

 the membrane, but gradually differentiation takes place 

 and the new parts of the limb are laid down in miniature. 

 As they increase in size they grow outward, and form a 

 small papilla on the stump. 



MUSCULAR SYSTEM. 

 (Pis. Ill, IV). 



Muscles of the Cefhalothorax. 



I. Eye. The ocular peduncle consists of two parts 

 — an inner rod-like portion extending inwards as far as the 

 middle line, and an outer swollen portion at the free end 

 of which is the visual organ. The outer portion articulates 

 with the inner, and is connected with the latter by means 

 of a flexible membrane. The movement of the outer 

 portion is effected by two small muscles — a ventral flexor 

 and a dorsal extensor. 



II. First antenna. The muscles are extremely 

 small. The basal segment of the protopodite has a dorsal 

 extensor and a ventral flexor. In their natural condition 

 the second and third segments are flexed. In both cases 

 the extensor is on the inner side and the flexor muscle is 

 on the outer side. 



