468 Reviews — Monsieur N. Jakowlew — 



II. — " Ueber die Morphologie und Morphogenie der Eugosa."' 

 On the Morphology and the Morphogeny of the Eugosa. By 

 N. Jakowlew. From the " Verhandlungen der Eussisch- 

 Kaiserlichen [Mineralogischen Gesellschaf't," Bd. xli, Lief 2. 

 St. Petersburg, 1904.] 



IN a paper under the above title N. Jakowlew deals with the 

 structural peculiarities of the Eugose Corals, seeking to explain 

 these peculiarities in the light of possible relationships between 

 the Eugosa and the Hexacorals. 



The most remarkable characteristic of the Eugosa compared with 

 the Hexacorals is their bilateral symmetry, of which the chief 

 expressions are the bent corallum, the presence of a main septum 

 (' hauptseptum '), and of a fossula (' septalgrube '). 



As many as four fossula have been claimed as occurring in some 

 forms of Eugosa, but it is shown that the depressions at the alar 

 septa (* seitensepten ') are not to be distinguished by any morpho- 

 logical difference from other interseptal loculi, so that no fossula 

 occurs except in the plane of symmetry of the coral. Nor can any 

 instance be found of two fossulai occurring in the plane of symmetry. 

 And when one occurs, the septum situated in it has always been 

 found to be the main septum. Therefore the presence of a fossula 

 always indicates the presence of the main septum. 



Some would define the main septum as that primary septum which 

 occurs on the convex side of the coral. Nicholson is quoted as an 

 author who does so. It is shown, however, that the peculiarities 

 which distinguish the main septum are the behaviour of the other 

 septa towards it, as shown by their outcrops on the surface of the 

 corallum after the epitheca has been removed. From this aspect 

 the outcrops of the secondaries are seen to be pinnately arranged 

 with regard to that of the main septum, and parallel to that of the 

 counter septum (' begenseptum ') ; also those between the alar 

 septum and the main septum (i.e. those in the main quadrants) are 

 parallel to the former, while those between the former and the counter 

 septum (i.e. those in the counter quadrants) meet the alar septum 

 at an angle. Again, the outcrops of the secondary septa in the main 

 quadrants meet the plane of the mouth opening (or, what is the same 

 thing, the lines of growth) at an oblique angle, while those in the 

 counter quadrants meet the lines of growth at right angles. 



Thus defined, the main septum is found to occur, often in the 

 same genus, now on the concave and now on the convex side of 

 the corallum. That is to say, the two chief expressions of bilateral 

 symmetry in the Eugosa (the presence of the fossula having been 

 shown to be bound up with that of the main septum), namely the 

 bending of the coral — what might be called ' external bilateral 

 symmetry ' — and the presence of the main septum — what might 

 be called ' internal bilateral symmetry ' — occur independently of 

 each other. The question naturally arises, which appeared first ? 

 Whether the bending caused the bilateral symmetry, or whether 

 "the bending .... arises from a tendency in the coral 

 towards bilateral symmetry." 



