68 



ACTINIAKIA 



The proximal part is rounded and fusing into the middle without distinct outline. No distinct physa 

 is present. The scapus is provided with a sometimes thin, sometimes thick, but translucent, often irregularly 

 wrinkled cuticle, to the outside of which small grains and a great number of detritus-particles are attached. 

 Under low magnifying powers small papilliform elevations are to be seen, which are, however, not regularly 

 arranged, they are as yet only thickenings of the ectoderm as may easily be ascertained on sections (text- 

 fig. 83). The capitulum is short, not thickened between the insertions of the mesenteries. The tentacles are 

 12 in number, probably arranged in two cycles; the oral disc is inconsiderable. The actinopharynx is short 

 and furnished with 8 longitudinal ridges. Whether a ventral siphonoglyphe is present or not I cannot decide 



with certainty. 



Anatomical descrip- 



) ' ~^~\ 

 ( /Y*~\^ t i o n : The scapus-ectoderm 



is as a rule not high, 

 here and there it is, how- 

 ever, thickened, cushion- 

 like. In these thickenings 

 the nematocysts are accu- 

 mulated (textfig. 83 n). 

 They are, however, not 

 numerous, but the groups 

 still must be regarded as 

 weak batteries of nemato- 

 cysts. The size of the ne- 

 matocysts is 29 36 X 3,5 

 5 //. The scapus is cove- 

 red with a folded cuticle, 

 now thin, now thick. If the 



cuticle (textfig. 83 c) is thick, it resembles the same layer in Isoedwardsia; it is only a little stained, or not at all 

 so, with borax-carmine which is easily absorbed by the mesogloea. The mesogloea is thinner than the ectoderm. 

 In the endoderm of the column I have observed large nematocysts. Whether these latter are normal com- 

 ponents of the endoderm I cannot with certainty decide. The circular muscles of the column are weak. The 

 ectoderm of the capitulum is thicker than the mesogloea. The ectoderm of the tentacles is high and contains 

 very numerous, closely packed spirocysts of variable size. The largest are of the same kind as those of the 

 column, but more sparse and 34 36 x 3,5 5 ;i in size. The ectoderm of the actinopharynx is high in the 

 ridges ; the rather numerous nematocysts show a distinct basal part to the spiral thread and reach a size of 

 3436 x 3,5 5 f i. 



The number of the mesenteries is 12 of which only 4 are weak off-shoots in the most distal part. 

 The longitudinal muscle-pennons of the 8 " Edwardsia-mesenteries" are not strong in the reproductive region 

 and show in transverse-sections about 10 low folds, all of about equal height or gradually shortened in the 



Fig. 85. 



Textfigs. 83 85. Milne-Edwardsia nathorstii. 



Fig. 83: Transverse Section of a portion of the scapus (compare 

 text!). Fig. 84: Transverse section of a perfect mesentery in the 

 reproductive tract. Fig. 85: Transverse section of parietal muscle. 



