Mr. W. S. Kent on the Emhryology of Sjponges. 151 



sometimes effected *. The abnormal and, in some instances, 

 prodigious comparative size of the amoeboid masses from which 

 the ciliated embryo is developed admits, however, of a second 

 interpretation. As shown by Haeckel in many of his illustra- 

 tions (a portion of one of which, representing his Ascaltis 

 cerebrum, is here reproduced, Plate VII. fig. 12), the external 

 border of the amoeboid mass is invested by a continuous and 

 even layer of the normal flagellate monads. Now it has been 

 demonstrated by me in my communication on this same subject 

 to the Linnean Society last year, and has since been confirmed 

 by repeated subsequent observation, that the amoeboid particles 

 or cytoblasts stationed within the substance of the syncytium, 

 and which later on, under normal conditions, assume the 

 typical collar-bearing form, receive their sustenance through the 

 flagellate types, which, having filled themselves to repletion, 

 pass all additional supplies, arrested by the hyaline collars, 

 through their own bodies into the syncytium, where the 

 same are at once seized by the amoeboid particles. By a similar 

 process it is not improbable that certain of these large amoeboid 

 masses, as indicated in the figure quoted, represent ordinary 

 cytoblasts or imperfectly developed flagellate zooids, upon 

 which the task of conversion into the ciliated swarm-gem- 

 mules specially depends — to which end they are, as it 

 were, specially fed and fattened up by the superincumbent 

 flagellate units. The falling-off or diminishing amount of the 

 food supply might, under these conditions, arrest at any stage 

 the further development of these amoeboid masses, causing 

 them to enter upon their final transformations at different 

 epochs of growth, which would thus sufficiently explain the 

 variable calibre of the ciliated bodies produced by subse- 

 quent segmentation f . 



From the account now submitted of the developmental 

 manifestations of the so-called ciliated sponge-embryo it is 

 clearly evident that we have here represented merely a mode 

 of increase, for a special purpose, by multiple fission, differing 

 in no essential manner from that common to Magosphmra and 



• Haeckel furtlier describes and figures the coalescence of numerous 

 individuals into one homogeneous amoeboid mass of his simple monad 

 form Protomyxa as a prominent feature in the developmental cycle of 

 that type. 



t That this suggested interpretation does not in any way militate against 

 the conception of the unicellular and Protozoic nature of the essential 

 Spongozoa is sufficiently demonstrated from the fact that among certain 

 colony-forming higher ciliate Infusoria, and notably the genus Zootham- 

 nimn, special zooids are at times developed for a closely parallel object, 

 and attain, in comparison with the ordinary units, an equally dispropor- 

 tionate size. 



