94 



LOWER INVERTEBRATES. 



the bell walls of such a form that when looked at above, it seems more like a cyst sur- 

 rouiuling it than a hood serving as its cover. From the inner walls of the bell, 

 hanging into the liell cavity, there are placed sixteen dark-brown j)igmeuted bags 



wliich lie in a cii-cle with a radius about one-thiid 

 of that of the bell. Although the function of 

 these bodies is luiknown, it may be predicted that 

 they will be found to serve as receptacles for 

 the elaborated food eaten by the medusa. The 

 stomach of Unerges is very simple in its structure 

 and never hangs out.side of the cavity enclosed 

 liy the bell walls. While the jelly-fish is in the 

 act of swimming, the marginal bell lappets are 

 commonly folded inward, forming a notched veil 

 which distantly resembles the so-called velum of 

 the hydroid medusa. At one time in the his- 

 tory of the nomenclature of the jellj'-fishes, the presence or absence of a veil was 

 used in designating the two great groups into which the medusie were divided. The 

 term Craspedota refers to those in which a Avell-marked velum is found, the Acraspeda 

 where the same is absent. The Hydroidea and Siphonophora are craspedote, the Dis- 

 cojjhora are supposed to be destitute of a veil, and are therefore acraspedote. 



Of the many aberrant families of the Discoj)hora, none differ more widely 

 from the genera which we have already considered, than that of the Lucekxakid-E, 

 or Calycozoa as they are sometimes called. In Lucernaria., the best known genus 

 of this family, we have a trumj)et-shaped animal of comparatively gmall size, which 

 is attached by the smallei- end, but has the enlarged extremity free. The free end 

 has a disk-shaped form, and in the centre there is an opening into the body cavity 

 which is the stomach. Around the edge of the disk there are arranged at intervals 

 eight bundles of short tentacles or tentacular bodies of doubtful function. TJie body 

 walls of one of our common species has a greenish color. 



Several theories of the relationship between the Lucernaridie and the other 

 Discophora have been suggested, and their relations to this group are not recognized 

 by all naturalists. Of these theories tiiere are two which seem to the 

 writer the nearest approximations to truth in regard to the affinities of 

 the family. Several naturalists, considering the attached mode of life 

 of Zucernaria, but nxore especially its anatomy and what little is 

 known of its development, have supjjosed that iMcernaria is in 

 reality an adult in an :u-rested form or stage of development, and 

 that its nearest ally must be looked for in the young of other Disco- 

 phores. The young of many genera jtass through a condition in the fig. e 

 progress of its development when it is attached to the ground, and 

 the allies of Liicernaria are by many naturalists recognized in these forms. 



A second interpretation, suggested by E. Haeckel, has even more plausibility than 

 that already mentioned. It has this in its favor, that it refers the Lucernaria to the 

 adult and not to the j-oung of another genus. A beautiful medusa was found by 

 A. Agassiz and by the Fish Commission in the Gulf Stream, and has been referred to a 

 genus long ago described mider the name Periphijlla. Periphylla is in fact a type 

 of a family called the Peeipiiyllidjs, and is in many respects one of the most aberrant 

 of the many genera which make up the Discophora. 



