134 KEPORT — 1871. 



Aealephs is no longer an exception to the simultaneous appearance of all the 

 types of Radiata in the lowest fossiliferous formations, and the peculiar cha- 

 racters which these old Hydi-oid corals present appears in a new and very 

 instructive aspect." 



A. Agassiz includes the Tabulata amongst the Hydrozoa. He notices 

 " that the absence of radiating partitions in the Tabulata seems to show 

 without much doubt that their true place is among the Hydroids." It is 

 true that Prof. Agassiz has not observed the Medusa-buds on the specimens 

 he has figured, yet the Hydroid character of the animal and their similarity to 

 I[aIochcens-]ike Hydroids is very striking (Havard Catalogue, 1865, p. 219). 



Prof . Alexander Agassiz informs me that his father still holds these opinions, 

 and that new researches have satisfied him about the correctness of the 

 di'aAvings which have been lately reproduced. '•' MiUeiJora is not an actinoid 

 polyp, but a genuine Hydroid, closely allied to H)jdractinia." 



This very strong expression of opinion is founded iipon the appearance 

 presented by the polyps of Millepora cdcicornis, the drawing of which has 

 been reproduced by A. Agassiz. Now the distinction between the Actinozoa 

 and the Hydrozoa is well marked ; in the first the generative apparatus is 

 included in the gastric and perigastric cavities, and in the last the digestive 

 and generative organs are perfectly apart. Every variety of tentacular and 

 disk apparatus may exist in either, but the external development of the gem- 

 mules, ova, and embryonic forms must be recognized before any Coelenterate 

 animal can be associated with the Hydi'ozoa. 



Here is the point at which Agassiz faUs. His researches are only sug- 

 gestive, until the generative organs are recognized on the protruded polypes 

 of Millepora, and until the mesenterico-ovarian layers are proved not to exist 

 ■within the cahces. The external resemblance of the Milleporc polypes to the 

 sterile Hydractinia is evident. 



The remarks upon Pavositidse, Sideropora}, and other genera, made by 

 Agassiz in consequence of the assumption that Mdlepora is Hydrozoan, are of 

 doubtful value ; and I must refer back to my analysis of the Tabulata to show 

 how a confused classification between both classes imperils research. Sidero- 

 2)ora is not a tabulate form even. A careful examination of Columnarla satis- 

 fies me that Agassiz's description of the lamellae fails in that genus ; and inas- 

 much as the wavy lines of Gorgonia and CoraUium are connected with the water 

 system of the species, they can have no possible relation with the radiate 

 amellfe or groovings of the MiUeporan calices. The homologucs of the grooves 

 are the depressions and irregular interstriatcd portions on top of the ccenen- 

 chyma between the calices in the Tabulata. 



The perforate walls and the septa of the true Favositidae seem to remove 

 them from the range of the remarks of Agassiz, which may well deserve 

 attention, so far as Millepora is concerned, for it is a genus with^ marked 

 distinctions from all other corals. 



It is not reasonable to include the Rugosa, because some of them have no 

 tabulic, and others have them so much like dissepiments, or associated with 

 dissepiments, that we are impressed with the unimportance of the differen- 

 tiations established by the presence of horizontal tabukic!. 



It is most important that the minute structure of the MiUeporidae should 

 be thoroughly investigated, and any report on the Palaeozoic corals must be 

 very incomplete -ndthout a detailed description of its study. 



