223 



AMPHIPHOLIS KOCHII LUTKEN 



Spawned eggs oi A. kochii are 100 |im in diameter, opaque and slightly 

 brownish. After 6.5 hrs of development, the early blastula appears, which is 

 spherical and covered with a transparent, hyaline membrane through which 

 cilia protrude. Soon the shape of the blastula changes; it becomes oval and 

 elongates along the animal-vegetal axis. The gastrula forms after 20 hrs of 

 development. It is somewhat flattened laterally, retains the hyaline mem- 

 brane, and its surface is uniformly covered with cilia. After 25 hrs of devel- 

 opment, the gastrula forms a crest and then acquires a triangular shape. After 

 some time, it is possible to distinguish four axial spicules, rudiments of the 

 larval skeleton. 



Pluteus I Stage 



After 42 hrs of development, the early pluteus is formed. All the skeletal 

 rods in it are simple. At this stage, cilia are still retained over the entire body 

 of the larva but their length varies; the longest occur in the ciliated band and 

 at the basal end of the body. The crest is also retained. The entire larva is 

 opaque and reddish-brown. The hyaline membrane persists but its thickness 

 reduces considerably. In live specimens the skeletal rods are poorly visible, 

 at the 49th hr of development, the posterolateral arms increase somewhat in 

 length and their ends become transparent. The basal rods of the larval skel- 

 eton distally bear three prominent, short processes forming an analogue of a 

 lock. Cilia in the basal part of the body and the hyaline membrane are still 

 retained. The entire larva, except for the ends of its posterolateral arms and 

 the loop of the ciliated band of the oral region, is reddish-brown (Figure 1 72). 



When the pluteus dimensions reach 350 |J.m x 165 |a.m, the skeletal rods 

 begin to show minute spines. The lower process of the basal rod elongates, 

 its length reaching 25 |im. At the tip it becomes biftircate. The larval body 

 in the region of the processes is drawn towards the ventral side. The reddish- 

 brown color disappears but the hyaline membrane is still intact at places. 

 Cilia of the basal part of the larva disappear. When the larva dimensions 

 reach 400 |j.m x 200 |j,m, the rudiments of the posterolateral arms become 

 visible. The rods of these arms, as also the entire skeleton, are simple. At 

 dimensions of 450 |im x 250 |j.m, the lateral processes of the basal rods of 

 the skeleton elongate and form a rhombic structure, but do not fuse into a 

 single complex. At this stage, the hyaline membrane still persists at some 

 places, although its thickness reduced very significantly. 



At dimensions of 500 |im x 300 |im, the posterolateral arms in the 

 pluteus become especially elongate and orange pigment granules begin to 

 appear along their spines. The hyaline membrane disappears completely. 



