NATURE AND AFFINITIES OF THE SPONGES. 177 



substance of the cytoblastema contributes largely towards the augmentation 

 of the common colony, it evidently does not provide for the more remote 

 dispersion of the species. This is effected in an entirely distinct manner. 

 In many cases, such as that of the common fresh-water Spongilla, such a 

 desired result is partly brought about by the production of encapsuled 

 gemmules, or so-called " seed-like bodies " at the time of the decadence 

 and disintegration of the parent stock. Practically, the development of 

 these reproductive bodies may be said to represent on a large scale a 

 modified process of encystment closely corresponding with the production 

 of sporangia among the Mycetozoa described on a preceding page. As 

 winter approaches, the zooids forming the parent colony assume an 

 amoeboid state and coalescing in spheroidal groups, secrete around them 

 a common spiculiferous capsule, within which they remain in a torpid or 

 quiescent state, until revivified by the return of spring and its accompany- 

 ing congenial temperature. A singular inversion of this phenomenon 

 obtains among the Spongilla of tropic countries, and in which, as recorded 

 by Mr. Carter of certain types occurring in the neighbourhood of Calcutta, 

 the production of gemmules, or entrance upon a hibernating or quiescent 

 state is resorted to (identically with that of many tropic fishes, such as 

 Lepidosiren] as a protective provision against the summer droughts, when 

 the tanks and reservoirs that they customarily inhabit are dried up. 



The quiescent or hibernating gemmules, however, play but a minor part 

 in the local distribution of the species compared with the actively motile 

 reproductive bodies produced as offgrowths by sponges of apparently every 

 denomination during their period of luxuriant growth. With these motile 

 bodies, indeed, the quiescent or hibernating gemmules are in no ways com- 

 parable, they representing more correctly composite modifications of the 

 temporary " protective encystments " of the ordinary Infusoria. As true 

 reproductive gemmules only are here recognized those free-swimming 

 bodies, the so-called " ciliated-larvae," or " ciliated sponge-embryos," first 

 discovered by Grant and Lieberkuhn, upon the correct interpretation of 

 which the minds of biologists within these latter days have been so 

 diligently exercised. It is upon these seemingly anomalous reproductive 

 structures, moreover, that Professor Haeckel has, as already stated, 

 conferred the distinctive title of gastrula, and sought to demonstrate 

 the conformance of the Spongida to the Metazoic type. Without recapitu- 

 lating the altogether erroneous interpretations first published, and quite 

 recently maintained, by Haeckel concerning the form and structure of these 

 bodies, reproduced, rather as an admonition and warning than for the pur- 

 poses of edification, in the woodcut illustration with its accompanying 

 description at page 157, a brief examination of the more reliable data accu- 

 mulated through the independent investigations of Metschnikoff, Oscar 

 Schmidt, F. E. Schulze, Barrois, and other recent authorities may be 

 proceeded with. While one and all of them are unanimous in condemn- 

 ing, as entirely fallacious and untrustworthy, that special bilaminate and 



N 



