METAMORPHOSIS. 



71 



(Fig. 33 B), their number being increased by the addition of new 

 rudiments, the point at which the budding of tentacles first takes 

 place being the most anterior or distal part of the lophophore, which 

 later becomes its dorsal part. 



R B __ 



FIG. 33. Two older ontogenetic stages of Argiope (after KOWALEVSKY). a, eye-spots ; d, mid- 

 gut ; oe, oesophagus ; st, peduncle ; t, tentacle-rudiments. 



It may at first sight appear remarkable that the tentacles grow 

 out on the inner side of the mantle-lobe. But if we consider the 

 free-swimming larva, in which this inner side still functions as 

 the outer side of the thoracic section, we shall see that the crown 

 of tentacles here has a similar post-oral position as in the Adino- 

 trocha (cf. diagram Fig. 34, t). 



v ' 



FIG. 34. Hypothetical scheme of the metamorphosis of the Brachiopoda for comparison with 

 the Actinotrocha. A, free-swimming larva. The oral aperture (m) is depicted, although not 

 actually present at this stage. The position in which it here appears, below the cephalic 

 lobe (k), is not in accordance with KOWALEVSKY'S statements. The tentacle-buds also are 

 not actually present at this stage. B, an imaginary transition stage. C, younger Brachiopod 

 after the reversal of the two mantle-lobes. The epistome has arisen from the cephalic lobe 

 (k). The row of tentacle-buds (t) belongs for the most part to the dorsal lobe of the mantle. 

 d, dorsal lobe of the mantle ; ep, epistome ; k, cephalic lobe ; m, mouth ; st, peduncle ; 

 t, tentacle-buds ; v, ventral lobe of the mantle. 



