1884.] 99 [Hyatt. 



central cavity or archenteron, which also reappears at the same 

 time. 



Haeckel's definition of the individual or j^erson among sponges, 

 as a single ascon or a branch with a single cloacal aperture is, 

 therefore, only true in the Ascones, and cannnot be true in any 

 fleshy sponge. No Sycones, Leucones, or carneospongian can have 

 a branch springing from a true bud, or spongozoon. Such a branch 

 is not a single ampulla, with its proper walls and cloacal crater 

 but consists of a number of such, and is compound from the start. 

 Thus it becomes plain by means of the embryology and the 

 morphology that these compound branches are merely extensions 

 of the general surface remotely like an arm or a leg, but not 

 spongozoons. 1 A branching carneospongian is not, therefore, a 

 colony, but must be regarded as an individual with a body so 

 plastic and susceptible to the influences of the surroundings as to 

 vary from a sheet, or a solid lump to a more or less irregularly 

 symmetrical branching form in many species according to the 

 locality in which it grows (Microciona and Spongia). 



A very graphic account of this problem is given by Yon Len- 

 denfeld in his Monogr. Australian Sponges and there he calls 

 attention to the remarkable cases of zoa-impersonalia, or what we 

 should consider as degraded colonies. One example is the Apy- 

 silla violacea (Zeitschr. Wissen. Zool., vol. xxxvin) in which the 

 individuals or zoons coalesce and consequently may spread over 

 many square meters in the waters of Port Philip. Cases of this 

 kind are common in embryos and were first described by 

 Oscar Schmidt ; and Potts has recently shown them to be com- 

 mon between the young arising from the statoblasts of Spongilla. 

 All such cases belong to the phenomena of coalescence, and do 

 not at all effect the foregoing conclusions except so far as they 

 show that the sponges are very primitive and peculiar forms. 

 Nor do the independent buds of Tethya or Halisarca, which we 

 take to be more or less similar to statoblasts in their nature, 

 have any bearing upon our statements, which relate only to the 

 peculiar modes of branching prevalent in Porifera. 



Vosmaer regards the extension of the cavity into branches as 

 being due to the advantageous nature of the change, and Polae- 



1 Johnson's Encyclop. supplera. appendix, p. 1668, 1878, contains a statement of 

 this result, but not of the reasoning which led to it. 



