630 REVIEW. 



solved in 30 per cent, caustic ammonia, and are probably 

 vegetable. 



In the case of the sheath on the apical ray of gastral 

 spicules, Dendy most justly says that there is no evidence to 

 prove their mesodermal origin, and I differ from him in that I 

 am thoroughly prepared to accept them as endoderm. The 

 time has come to free the study of the Porifera from the fetish 

 of mesoderm, and to render to her grasp only that to which 

 embryology can prove her entitled. The presumption lies in 

 favour of the old layers, the ectoderm and endoderm ; the 

 onus probandi is on the new-comer. 



My own work has led me to regard the endoderm not only 

 as multiform, but as most proteic. Dendy recognises it as 

 "' polymorphic," but this appears only to refer to the relative 

 state of " retraction" of the collars and flagella. I agree with 

 all his description and figures of these, both in this and preced- 

 ing communications, and I have now myself observed, in the 

 living Sycandra raphanus, the coincidence of flagella and 

 SoUas's membrane which (in Halichondria p an ice a) he was 

 the first to meet with. But I have come to the conclusion that 

 this coincidence is only transitory; and while he most generously 

 yields priority for the theory of filtration, I have been brought 

 to relegate it to the disunited collars, and to believe that the 

 membrane of Sollas is a valvular adaptation to prevent the 

 reflux of water past satiate and therefore inactive cells. Where 

 he writes "retraction " I would write "disappearance," and I be- 

 lieve that in the old '• Verwandelung der Geissel bevvegung ^' in 

 *' Amoeboide Bewegung " lies the key to many of the anomalies 

 of the intimate structure of sponges. He draws and describes 

 in Leucosolenia cavata "yellow granules," which he more 

 than suggests are symbiotic algse. I have worked at them — 

 besides in former years — during the last nine months in Ascetta 

 clathrus (where, besides the description he quotes from Bower- 

 bank, they were described and figured by Metschnikoff, loc. cit.) 

 and A. primordial is. I find Dendy's drawings and descrip- 

 tions of their behaviour and relations most accurate; inAsc. 

 clathrus there is an additional point of interest that the 



