u6 



ACTINIARIA 



Textfigs. 144 145. 

 Siphonactinopsis laevis. 



Fig. 144: Transverse section of mesentery in 



the reproductive tract. Fig. 145: Transverse 



section of the outer part of a mesentery. 



well developed, almost as long as half the length of the column or, at any rate, more than one third of it, 

 and provided with numerous high folds. Only one siphonoglyphe is present at the ventral directives, it is 

 distinguished from the other furrows in the actinopharynx by its larger breadth and shows no aboral pro- 

 longation. 



Anatomical description: The proximal part of the column is as far as I can see of usual 

 structure. In the very few fragments left of the ectoderm of the column I have found very sparse nema- 



tocysts, about 14 17^ in length. Just 

 below the tentacles and above the crene- 

 lations on the column fragments of the 

 ectoderm were left. In these fragments 

 I observed closely packed nematocysts 

 and very sparse spirocysts, the latter 

 possibly belonging to the ectoderm of 

 the tentacles. These nematocysts were 

 a little larger (17 20 p. long) than those 

 of the other part of the column. Pos- 

 sibly we here have to do with pseudo- 

 acrorhagi, the occurrence of which can- 

 not, however, be added to the diagno- 

 sis, until it has been stated on better 

 preserved material than mine. The cir- 

 cular muscles of the column are weak 

 and form no sphincter. The ectoderm 

 of the tentacles contains numerous spi- 

 rocysts, 36 38X5//, and nematocysts, 

 22 29 X 2 fjt in size. The longitudinal 

 ectodermal muscles are well developed, 

 with palisade-shaped folds. The oral 

 disc is of the same structure as the ten- 

 tacles, the nematocysts are, however, sparser. The ectoderm of the actinopharynx is of ordinary thickness 

 and much thinner than the mesogloea. The granular gland-cells are very numerous, the typical nemato- 

 cysts less so and about 28 X 34 fjt in size. Besides these, there are here nematocysts with discernible basal 

 part to the spiral thread. They are about 24 p long and 5 n broad in their broadest end. I have here and 

 there found a spirocyst of the same size as that of the tentacles. The nematocysts and the gland-cells are 

 much sparser in the siphonoglyphe than in the actinopharynx. The mesogloea of the column and of the 

 other parts of the body is rather thick. 



The mesenteries are arranged in 20 pairs (10 -f 10), of which 2 are directive mesenteries. All mesen- 

 teries are perfect, fertile and coalesced with the actinopharynx in its whole length. It is difficult to decide 



