52 T. KOMAI: STUD^S ON TWO ABKKRANT CTENOPHORES 



condition of the sense-ortran is nearly the same as depicted in Ph 7, fig. 

 20 of Chun's monograph or in PI. 2, fig. 3 of Mortensen's paper ('12). 

 When viewed from above, the organ has a rhomboidal outhne with the 

 longer diameter in the sagittal plane of the larva. The part at the 

 ends of tlie diameter represents the rudiments of the polar plates. They 

 are defined from the more centrally situated parts very vaguely as yet; 

 in some later stages, however, they come to be marked off quite clearly 

 from the latter. The otoliths {ot) lie as aggregates of four or five 

 granules, one at each end of the shorter diameter. The sense-organ 

 still lacks the ciliary covering. The ribs are arranged in four close 

 pairs, each row comprising six or .seven comb-plates with very short 

 cilia. The rudiments of tentacles appear on the surface each as an 

 elongate oval area with both the aboral and oral ends elongate into 

 short processes. The entire area may be distinguished into a central 

 and a peri})heral part, of which the former is depressed slightly below 

 the general surface of the body, while the latter is raised a little 

 above it. In the side view of the larva on the tentacular plane (fig. i), 

 the inner margin of the tentacles describes an arc which stretches 

 from beneath the sense-organ to the oral end of the oval area on the 

 surface. 



The mouth is nearly round and small as yet. The pharynx {ph) 

 which the mouth leads into presents also a roundish outline in the 

 optical cross-section. The internal end of the pharynx is situated nearly 

 midway between the oral and aboral poles of the body, where it bears 

 a short prominence indicative of the oesophagus {oe). The endoderm 

 consists of four pouches situated interradially, the boundaries of which 

 show through clearly in the oral \iew of the larva as two straight lines 

 intersecting cruciatel)-. The larva rotates very actively within the egg- 

 membrane by means of the cilia of the ribs. 



Some of the larv^ae of this stage were fixed with P'lemming's 

 solution, imbedded in paraffin and sectioned. The shortage of available 

 material as well as the difficulty of imbedding prevented me from 

 obtaining good .sections. Nevertheless, figs. <S-I2, which represent some 

 of the .serial sections made apjjroximatcly transverse, though somewhat 

 oblique, to the vertical axis, will give an idea of the structure of the 

 larva in this stage. The epidermis is rather thin and very simple, showing 

 as yet no gland cells whatever. Each comb-plate is made up of three 

 or four longitudinal rows of columnar cells, four or five times as tall as 

 the iicighb(juring epidermal cells, with the plasm ajipearing somewhat 



