652 SUMMARY OF CURRENT RESEARCHES RELATING TO 



importance. The sac is frequently found in zocecia whose polypides 

 have undergone histolysis. 



The floor of the compeusation-sac corresponds in whole or in part 

 with the memhranous frontal surface ("frontal membrane") of a Mem- 

 branipora ; and its muscles are homologous with the parietal muscles of 

 the same genus. It appears to have been evolved in more than one 

 way. 



In Cribrilinidse a calcareous wall ("frontal shield") is developed as 

 a series of marginal spines, which overarch the frontal membrane. This 

 leads to the condition found in some Escharine forms, in which, as in 

 Umbonula, the calcareous frontal shield similarly overarches the frontal 

 membrane. 



The frontal shield of the Microporidaj and Steganoporellidre is of 

 the nature of a " eryptocyst," i.e. a calcareous lamella which grows hori- 

 zontally across the body-cavity beneath the frontal membrane. This 

 has, perhaps, led to the condition found in Lepralia, Schizoporella, &c. 

 in which the compensation-sac is developed as an invagination at the 

 base of the operculum, and passes to the deeper side of the frontal 

 shield, which is on this view a cryptocyst. 



The epitheca, or layer of living tissue, bounded by a cuticle, which 

 covers the frontal shield, may represent the entire frontal membrane 

 (Microporidee, &c), or only a part of that membrane (Lepralia, &c), or 

 it may have l>een derived from the outer calcareous layer of the frontal 

 bars of a Cribrilina-like form (Umbonula). The epitheca is frequently 

 responsible for the addition of secondary calcareous matter to the frontal 

 shield, and in some cases (Cellepora, &c.) for the formation of new 

 generations of zocecia which are superposed on the older ones. 



The operculum, in its more primitive condition, is merely part of the 

 frontal membrane strengthened by a semicircular marginal flange. It 

 acquires a firmer texture and a more elaborate arrangement of its 

 thickened parts as the result of its articulation with calcareous portions 

 of the zooecium. While occlusor muscles may be regarded as an essential 

 adjunct of the operculum, definite divaricators seem to have been evolved 

 as a modification of the distal pair of parietal muscles. 



The consideration of the relations of the frontal surface involves 

 some rearrangements in the classification of the Cheilostomata. 



The results of the study of the compensation-sac and frontal surface 

 generally are confirmed by an examination of the primary zucecium or 

 " ancestrnla " (Jullien). 



Contributions to the Anatomy of Rhabdopleura normani.*— A. 

 Conte and C. Vaney have studied well-preserved specimens^ of this 

 interesting animal, colonies of which were found by Prof. R. Kcehler in 

 Lophohelia prolifera. 



Their most important results are the following :— (1) the testis and 

 the ovary arise from differentiations of the two extremities of the stalk ; 

 (2) the space enclosed between the wall of the body and the internal 

 organs is occupied by a trabecular connective tissue ; it is not sub- 

 divided by septa, and it cannot be regarded as homologous with a body- 

 cavity; (3) there is not really any notochord. 



* Comptea Reudus, cxxxv. (1902) pp. 63-5. 



