MEDUSA I. 



75 



are mature, partly even spawned (see below); thereafter the umbrella continues its growth, whereas 

 the stomach does not further increase in size. 



To the measurements presented in the tables VII and \'III one may object that it is difficult 

 to measure the umbrella exactly, becau.se it is very contractive and may, at the preservation, be con- 

 tracted to a very different degree. This objection is entirely correct, and we must, therefore, take a 

 certain reservation to the figures of the tables. But, on the other hand, the difference between the 

 Icelandic and the P.ritish specimens, as shown bv the figures of the tai)les, both with regard to the 

 diameter of the stomach and the number of the radial canals, is so obvious that it can hardlv be due 

 to erroneous measurements owing to different contraction of the umbrella. .Moreover, when reo-ardino- 

 the absolute figures of the dimensions of the stomach, which can be measured fairly exactly, we will 

 find that in most of the Briti.sh specimens the stomach is actually larger than in the Icelandic 

 specimens. And a comparison of the two tables (VII and VIII) will give the result that the individuals 



Table VIII. Correlation between Diameter of .Stomach and Umbrella 



o f Halopsis ocellata. 



from the area west of the British Isles have, generally spoken, larger stomachs and a smaller number 

 of radial canals, whereas the specimens from the waters south of Iceland have smaller stomachs and 

 a larger number of radial canals, even quite setting aside the total size of the specimens. 



The young gonads are straight, but according as the sexual products are developed, the gonads 

 gradually become sinuous; this development commences, when the diameter of the specimen is 20 — 

 25 mm. When the individual is 30 — 35 mm wide the gonads are much thickened and greatly sinuous. 

 The male gonads may have up to 9 bends on either side; the female gonads never become so nnich 

 thickened or sinuous as the male ones. The maturity is reached, when the animal is about 35 mm 

 wide. Then, in the case of the female, we can see the eggs having penetrated the ectodermal epithe- 

 lium and being situated freely on the lateral walls of the radial canal.s, ready to be detached (Plate IV, 

 fig. 4; textfig. 7). When the male gonads become mature, they become much swollen and, besides 

 being sinuous, they get a finely wrinkled surface (Plate IV, fig. 3). — After the ripening and detach- 

 ment of the sexual products the animal continues its growth. According as the main part of the sexual 

 products are evacuated, the radial canals stretch and become straight again; at the same time the 



