BY R. VON LENDENFELD, PH.D. 335 



The great phylogenetic age of these nettling organs is made 

 likely by the fact that the Cnidoblasts are met with already, in 

 the free swimming larvae of some species, which is to be considei'ed 

 more as an exception than as the rule. This appearance of Cnido- 

 blasts in the larvae is probably produced by a very long-continued 

 heredity, as this happened in an analogous manner with the 

 mesoderm in the larvae of the Spongise, as mentioned above. 

 According to my idea, Cnidoblasts and their Homologa have been 

 developed in connection with the tentacles firstly in the adult 

 animal, as they have again disappeared in Beroe', together with 

 the tentacles (1) they are parts of these (according to Chun, modi- 

 fied muscular cells) which have been changed in such a remarkable 

 manner for purposes of catching prey. That they afterwards 

 should have attained the functions of defensive weapons, and 

 should then have been distributed all over the body does not 

 appear so very wonderful. (2) 



It is certainly difficult to ascertain whether the Sponges are — 

 as not possessing tentacles and Cnidoblasts — rudimentary in this 

 respect or not ; whether their ancestors possessed them or not ; 

 is not of very great importance, this does not seem to have to do 

 with the question whether the Sponges are Ccelenterata or not, 



In the ontogenesis of the Sponge we never find a stage where 

 anything homologous could be met with, just as little as we find 

 any trace of anything of the kind in the adult Sponge. But both 

 these facts do not prove that they really never had been present : 

 also here the ontogenetic image of the Phylogeny might be dirnned, 

 by a very long continued uselessness. It is, in case that the 

 Sponge-ancestors rarely possessed these organs, not difficult to 

 understand how they have been lost. 



(1) If Protohydra, accepted as an adult animal, had been as lively and 

 energetic as Beroe, also that animal could dispense with the protection of 

 Cnidoblasts if it had no mouth-arms. But, if in reality the tentacles were 

 the primary, and the Cnidoblasts the secundary thing, then Protohydra is 

 certainly not an ancestral but a rudimentary form. 



(2) Compare Cnidoblasts and their distribution among Ccelenterata, 

 Pagenstecher Allgemeine Zoologie, Band II., pp. 24-27 ; particularly Band 

 IV., pp. 259-263. Chun, Mikroskopische Waffen d. Coelenteraten, Humboldt, 

 Band I., Heft 2, 1882. 



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