STRllCTURK AND r)l':Vi:T,(")PMKN'r OF COKT.OriANA. 53 



clearer than tliat of the latter cells and the luiclcus large and located 

 in the basal part of the cell. 



The aboral sense-organ (s) is spherical in form and consists of 

 fairly tall columnar cells. The tentacular apparatuses are nearly the 

 same as those of the adult in every respect, save for that, the long and 

 contractile stem of the latter is represented by a very short and incon- 

 spicuous prominence {(. s). Each tentacular apparatus is enclosed within 

 a pouch-like depression, the rudimentary tentacle-sheath (/. s/i). The 

 inside wall of the sheath is thickened into the tentacle-basis which 

 consists of small cells arranged in strata four to six cells deep (d, ep). 

 The tentacle-basis is continued into the tentacle-root along the transverse 

 plane of the body, which piesents itself as a conspicuous crest-like 

 prominence directed towards the centre of the body and showing a 

 muscular characteristic. Towards the lateral sides of the sheath, the 

 tentacle-basis diminishes in thickness gradually and gives place to a 

 thin epithelium of an appearance perfectly identical with the ordinary 

 epidermis of the larva. 



The pharynx {pJi) is lined with tall cylindrical cells, as also the 

 oesophagus {pe) into which it communicates. The latter opens upwards 

 into the endodcrmal cavity representing the infundibulum {i). Unfor- 

 tunately, the histological condition of the endodermal parts of this stage 

 could not be studied clearly. 



As development advances, the body of the larva comes to present 

 a distinct lateral compression, growing broader in the transverse direction 

 than in the sagittal (fig. 5). The sense-organ (figs. 5-7; s) acquires the 

 ciliary covering. The cilia of the comb-plates grow much longer and 

 make the larva rotate more actively than before. In each tentacular 

 apparatus (/), the stem makes its appearance on the surface of the body, 

 at first as a tubercle-like prominence with some rudimentary colloblasts 

 scattered here and there on its surface. The mouth is widened consider- 

 ably along the transverse axis of the body. Both the lower and upper 

 halves of the pharynx show distinct lateral compression, but in directions 

 perpendicular to each other, the former elongate in the tentacular direc- 

 tion, and the latter in the pharyngeal. 



The lateral compression of the body already noted becomes more 

 prominent with development. At the same time, the region about the 

 tentacular apparatus is brought upwards to the same level as the sense- 

 organ (PI. I, fig. 5). Moreover, there appears a slight longitudinal 

 depression along each pair of the ribs, so that the body looks in the 



