MEDUSA. I. 



until tlie Medusa has at least trebled the original number of its tentacles". Only in very few cases 

 Browne found cord\li being converted into tentacles; on the other hand, I have observed several 

 cases of the same phenomenon in Staiiropliora mertensii. Plate III fig. 7 illustrates different stages of 

 cordyli being converted into tentacles in a specimen from Iceland. Fig. 7 a shows a normal cordylus 

 without basal bulb; in fig. b is seen a normal cordylus mounted upon a young bulbus; figs, c — f illu- 

 strate some stages of the further development into a young tentacle, the distal part of which is still 

 distinctly club-shaped; in stages, still further advanced, I have seen the bulbous terminal part in a 

 state of absorption. On the other hand, I have also seen numerous young tentacles with an entirely 

 pointed terminal part, tentacles which have, accordingly, never had any connection with cordyli. As a 

 result of my investigations I may state, I believe, that Browne's view of this question is correct, 

 though in species in which the marginal organs are very densel)' crowded, it will very frequently 

 happen, that cordyli are picked up by developing tentacles. 



According to Browne, the family Laodiceidce covo-'^xx^^^ the following genera: Laodicra^ Stauro- 

 phora^ PtycJiogcna^ Toxorcliis, Stanrodisctis^ and Mclicertissn. To these we may add, I believe, the genus 

 Chro7)iatoncma. Among the genera mentioned b}- Browne, I know only the three first by autopsy; 

 the three others I have never seen. I will, therefore, not enter into a general account of the compara- 

 tive morphology of the family. But from my studies on the species, represented in the material at my 

 disposal, I shall call attention to certain parallels to structures within the family TiaridcF, parallels 

 which, after my opinion, render it j^robable, that the Laodiccidcr have taken their origin from that group. 



One feature, common for the Laodiccida (the species examined by me) and the proper Tiaridcp 

 (the Nrofnrridir sensu Hartlaub) is the wide, open mouth tube, the free margin of which is more 

 or less crenulated (except in the lower forms among the Ttarid(r\ often complexly folded. The perra- 

 dial corners of the mouth is, in most forms, more or less drawn out into four lips. Another common 

 feature is the fact, that the manubrium is attached to the subumbrella along the arms of a perradial cross. 



In the Tiaridcp the gonads are developed into folds or grooves in the walls of the stomach. 

 Typically these grooves are arranged in the shape of four horse-shoes, the middle curves of which are 

 placed interradially on the upper (proximal) part of the manubrium, while the arms go downwards 

 along both sides of the perradial edges of the stomach. From this type the arrangement may be 

 further developed in a more or less complicated manner. In some of the Calycopsida- the horse-shoe- 

 shape has been obliterated, because no sexual products are developed in the interradial parts, the 

 gonads thus being arranged as eight adradial rows of sacks. 



A characteristic structure in many Tiaridce are the so-called "mesenteries", a double membrane 

 connecting a greater or lesser part of the perradial edges of the stomach with the radial canals. These 

 mesenteries are very ,differently developed in the different forms of Tiarida:. In the lower forms they 

 are quite absent; they are well-developed in such higher organized forms as Lcuckartiara^ Cafablema, 

 Neoturris^ Pavdea etc. If we imagine the mesenteries so far lengthened, that they reach as far down- 

 wards along the edges of the stomach as the gonads and, at the same time, just as far outwards 

 along the radial canals, and if we fancy, thereafter, that they become narrowed in a dorso-ventral 

 direction, the edges of the stomach will be drawn outwards towards the radial canals and, at last, 

 coincide with the latter. That is, in fact, what we find in Tiaranna rotunda and afjinis (figures of these 



