94 



LOWER INVERTEBRATES. 



Fig. 87, — Linerges tnercurius, thimble tisli. 



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

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

 hanging into the bell cavity, there are jjlaced sixteen dark-brown jjigmented bags 



which lie in a circle with a radius about one-third 

 of that of the bell. Although the function of 

 these bodies is unknown, it may be predicted that 

 they will be found to serve as receptacles for 

 the elaborated food eaten by the medusa. The 

 stomach of Ziinerges is very simple in its structure 

 and never hangs outside of the cavity enclosed 

 by 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 jelly-fishes, the presence or absence of a veil was 

 used in designating the two great groups into which the medusae wei'e divided. The 

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

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

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



Of the many aberrant families of the Discophora, none differ more widely 

 from the genera which we have already considered, than that of the Luceknaeidjs, 

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

 of this family, we have a trumpet-shaped animal of comparatively small size, which 

 is attached by the smaller 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. The body 

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



Several theories of the relationship between the Lucernaridse and the other 

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

 by all naturalists. Of these theories there 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 Lucernaria, but more especially its anatomy and what little is 

 known of its development, have supposed that JLucernaria is in 

 reality an adult in an arrested 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 pass through a condition in the fig. 88.— Zace?^ 

 progress of its development when it is attached to the ground, and """" »""™ "■ 

 the allies of Lucernaria 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 young 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 under the name Periphylla. Periphylla is in fact a type 

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

 of the many genera which make up the Discophora. 



