62 SUMMARY OF CURRENT RESEARCHES RELATING TO 



forms. The muscular cells have always more or less the characters of 

 epithelio-muscular cells, that is, of smooth, homogeneous, fusiform 

 fibres without nucleus, united to a cell. The connective tissue varies 

 from a finely fibrous condition to one in which the cells are large and 

 distinct, recalling the characters of fibro-cartilage. The muscular 

 system supplies no longitudinal muscles to the body-wall in Actiniaus, 

 and it varies little in them ; but in Cerianthus the longitudinal 

 muscles are present, and constitute that genus a distinct type. No 

 central nervous system was found ; but nervous cells and fibres occur, 

 and are especially abundant in Calliadis. The origin of the mesoderm 

 from the ectoderm is established. 



Structure of Corals and Sea-anemones.*— The brothers Hertwig 

 have concluded, from their studies of ActinicB, that the non- 

 Alcyonarian Anthozoa ( = Zoantharia of De Blainville and of Milne- 

 Edwards, or Helianthoidea of Latreille) should not constitute a single 

 order, but ought rather to be subdivided into several groups, each 

 equivalent to Ehrenberg's Octactinia. As an important character, to 

 be used for such subdivision, they suggest the structure and orienta- 

 tion of the mesenteries, with their associated muscles and genitalia. 



Herr G. v. Koch continues his previous researches on the same 

 subject. He first gives a revised list of the few groups in which the 

 arrangement of the mesenteries is precisely known, and adds the follow- 

 ing new observations : — 1 . In Caryoplvyllia cyathus the mesenteries and 

 their muscles behave as in the ordinary Actinire. Of the stony septa, 

 the older lie in the chambers, the younger are interlocular. The 

 " ventral " septum usually difiers from the " dorsal " in size. The 

 same is true of the composite Aporosa, e. g. Stylophora. 2. Madrepora 

 variabilis resembles Caryophyllia as to the arrangement of its 

 mesenteries and muscles. The terminal calices had six septa within 

 the (six) principal chambers, and six smaller interlocular septa ; these 

 last were absent, as a rule, in the lateral corallites. The dorsal and 

 ventral chambers answer to the two larger tentacles. The two 

 corresponding septa, which lie in one plane, tend to coalesce. 3. 

 Zoanthus (Palytlioa) axinellce displayed the same (which we now, 

 therefore, term the typical) orientation of the muscles. Koch's 

 specimens had usually thirty-two mesenteries. Of these, eighteen 

 bore filaments, and were inserted by their whole length along the 

 alimentary vestibule, whose upper region only gave support to the 

 other fourteen mesenteries, which were furnished with a free un- 

 thickened margin throughout the rest of their course. 



Koch has also re-investigated Cerianthus. Young individuals of 

 G. membranaceus displayed marginal tentacles so differing among 

 themselves in size as to suggest a law of succession for these organs 

 similar to that already noted by A. Agassiz. The marginal tentacles 

 of the same species of Cerianthus are also furnished with curious 

 longitudinal fissures. Each tentacle has a series of these fissui'es 

 disposed on its inward ( = axial) aspect. The fissures can be seen 

 with the naked eye. A single fissure is placed midway between every 



* Morph. Juhib. (Gegenbaur), vi. (1880) pp. 355-Cl (1 pi.). 



