MEDUSJE. I. 



79 



The gonads always commence at or very near the base of the stomachal peduncle (Plate IV, 

 figs. 9 and 10) without relation to the developmental stage of the individual. The distance from the 

 distal end of the gonads to the circular vessel, on the other hand, depends on the developmental stage. 



The female gonads are sinuous, with 23 bendings towards either side (textfig. 13 a). The male 

 gonads are thick, cylindrical, only provided with a single constriction or bend near the middle (textfig. 

 13 b), more seldom with a couple of bends (textfig. 13 c). In the gonadial part of the radial canals 

 the gonads occupy the lateral walls from the subumbrella nearly to the ventral edge, leaving only a 

 very narrow edge to separate the gonads of the two sides (see Plate IV, fig. 6, representing a trans- 

 verse section of a radial canal with male gonads). Plate IV, figs. 7, 8, 9, and 10 represent the female 

 gonads. It will be observed that the eggs are placed in the ectoderm in a single layer; fig. 7 is a 

 transverse section of a canal with unripe eggs; in fig. 8 the eggs are mature, and some of them have 

 penetrated the ectodermal epithelium; several eggs have already been detached; figs. 9 and 10 repre- 

 sent mature female gonads, the ripe eggs situated closely side by side on the outer surface of the 

 lateral walls of the canal, ready for deliberation. In 

 the gonadial part the radial canal is much com- 

 pressed laterally, having a high and narrow lumen. 



The size of the individuals, when the sexual 

 products become mature, is somewhat variable. In a 

 few cases I have found fully mature specimens being 

 10 12 mm wide, but as a rule the maturity does 

 not seem to be reached until the diameter of the 

 animal is 14 15 mm. I have seen female individuals, 



Fig. 14. Tiaropsis >nulttcirrata bars. Diagram, snowing the 



which have deliberated their eggs, with the following succession in the development of the tentacles. From a 



specimen, 1.5 mm wide, with 47 tentacles. 



diameters: 15, 16, and 18 mm (all from Iceland). 



The marginal vesicles and the ocelli have been examined by Bohm (1878) and Linko (190x5). 

 The concretions are, as a rule, placed in a single bow-shaped row; not seldom, however, one or more 

 of the concretions are pushed out from the row, so that there may even be two rows. The concretions 

 are large, globular, or somewhat angular owing to mutual pressure. They are placed closely side by 

 side. As a rule most of them are of equal size, only the outermost on both sides being smaller 

 (younger); not seldom there is a very tiny concretion at one of the outer ends of the row. Accordingly 

 the concretions seem to be formed and developed from the middle of the row outwards. 



A specimen from Trangisvaag, Faeroe Islands (locality No. 20 b in the list below), 1.5 mm in 

 diameter, has 47 tentacles, the sizes and arrangement of which clearly indicate the succession in which 

 the tentacles are developed. The facts are represented in the diagrammatic figure, textfig. 14. The dia- 

 gram agrees very well with that given by A. Agassiz (1863) for Tiaropsis diademata, though I am 

 not sure, whether No. 4 and 5 may not be of the same age. The position of the marginal vesicles 

 corresponds to that of a third series of tentacles, and possibly the marginal vesicles actually have to 

 be regarded as being homologous with as many tentacles. Thus the formula for the first 40 tentacles 

 in the present specimen is as follows: 4^ -- \t^ (+ 8 marginal vesicles) + i6/ s + 8/ 4 -f 8/ s , or, if t t and 

 / 5 are of the same age: 4/, + 4/ 2 (-J- 8 marginal vesicles) -j- i6/ 3 + i6/ 4 . -- The tentacles are densely 



