I 86 NATURE AND AFFINITIES OF THE SPONGES. 



enumerated, it has yet to be recorded that it very commonly happens that 

 these structures present an altogether irregular and asymmetrical contour. 

 Illustrations of such irregular formations, as figured by Oscar Schmidt, of 

 Grantia {Sycajidra) compressa, and as observed by the author, will be found 

 reproduced at PI. IX. Figs. 32 and 35. Such asymmetrically developed 

 gemmules may retain fundamentally the moruloid or amphiblastuloid 

 structural type, being in the one case composed entirely of similar and in 

 the other case of dissimilar constituents. The fact that these various 

 irregularly formed gemmules are by no means of rare occurrence, may 

 be accepted as furnishing supplementary evidence in demonstration of the 

 non-correspondence of these sponge-gemmules, or so-called ciliated larvae, 

 with the embryos of the typical Metazoa, and in which latter organic 

 series the production of asymmetrical germs is quite exceptional. One of 

 the strongest arguments furnished in support of the essentially Protozoic 

 significance of these reproductive bodies is, undoubtedly, afforded by the 

 independently contributed testimony of Oscar Schmidt and Metschnikoff, 

 by both of whom it is shown that in the case of Ascetta primordialis, 

 the component flagellate elements of the moruloid gemmule assume 

 quite independently an amoeboid .condition, and retiring separately into 

 the central segmentation cavity, undergo their further metamorphoses. 

 Ultimately, these separately retreating amoebiform units completely fill 

 up the central cavity, and burst through the posterior region of the 

 ciliated body, project at this extremity, and so produce in a roundabout 

 manner a pseudo-amphiblastula. It will be at once recognized that 

 while this peculiar developmental phenomenon of the sponge-gemmule 

 exhibited by Ascetta primordialis, is altogether opposed to anything that 

 obtains among the Metazoic series, it is at once reconcilable with a 

 Protozoic interpretation. With their near allies the simple flagellate or 

 collared monads, e.g. Phalanstcriiiin.Spongomoiias, -a-wd Protospongia, parallel 

 phenomena, including the assumption by the adult zooids of an amoeboid 

 state, and their retreat within the common gelatinous cytoblastema-like 

 matrix, or zoocytium, represents the normal reproductive process. 



The highly important evidence that demonstrates the thoroughgoing 

 Protozoic affinities of the sponge with relation to the primary origin and 

 development within the parent sponge-stock of the free-swimming ciliated 

 gemmules, has yet to be submitted. The initial condition of these repro- 

 ductive structures, as conceded unanimously by the independent testimony 

 of every investigator, takes the form of an amoebiform body, varying in size 

 from the i-3000th to the i-200th of an English inch, and presents a con- 

 siderable likeness to the primary condition of an ordinary ovum. With, 

 however, the interpretation of the significance and subsequent evolution of 

 this amoebiform structure that is most generally advocated, the author has 

 to declare himself entirely at issue. In accordance with this more widely 

 accepted view, the amoebiform body is a true ovum, developed separately 

 and independently in the interstitial substance of the sponge, and after- 



