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NATURE AND AFFINITIES OF THE SPONGES. 163and in that case amazingly remarkable isomorphism, the erasure of theirnames from scientific nomenclature, and also that of the entire Physemarianorder, will be rendered unavoidable. Most unfortunately for ProfessorHaeckel, the context of his essay under discussion upon the gastraea theoryin general, and upon the group of the Physemaria in particular, so aboundswith direct negations and manipulations of known facts in order to adaptthem to the requirements of his own hypotheses, that the verdict arrivedat by the most impartial students of this question must inevitably tend tocast discredit upon his representations even where the same are possiblycorrect. It is thus not a little surprising to find reproduced as the larvaltype of Haliphysema in this essay, the self-same erroneous accounts anddiagrammatic illustrations of his so-called " gastrula-larva " of the sponges,first formulated in his 'Monograph of the Calcispongiae,' and submitted atpage 157 of this volume.The same inversion of the anterior and posterior apices and accompanyingfallacious allocation of a gastric cavity, oral aperture, and evenlydeveloped external and internal cellular layers, is once more repeated,the larval forms of the Physemaria being made to correspond with a likealtogether hypothetic formula. The histologic characters of the essentialcollar-bearing flagellate cells of the sponge-body, assumed to be sharedby Haliphysema and its allies, are again materially reduced in order tomake them conform more nearly to the plan of ordinary tissue-cells, andwith the morphologic and functional value of which they are alone accredited.Professor H. James-Clark and Mr. Carter had already shown that thesepeculiar flagellate sponge-cells exhibited a very significant Protozoicfeature in the possession of two or more posteriorly located, rhythmicallypulsating, contractile vesicles. In his 'Monograph of the Calcispongiae,'Professor Haeckel grudgingly conceded and figured a single posteriorvacuole, but denied to it the property of rhythmical contraction, affirmingthat it was a mere non-persistent and unessential lacuna developed in theprotoplasmic substance of the cell. In that advanced exposition of thegastraea theory, however, embodied in his 'Biologische Studien' for theyear 1877, the contractile vesicle, or protoplasmic lacuna, is improvedaltogether off the morphologic landscape, and the essential flagellatesponge-cell now appears with a simply nucleated but otherwise undifferentiatedprotoplasmic body. In two instances only does Haeckel makeany concession to the antagonistic results arrived at by contemporaryexplorers in the same field of research, while even here these results arewith a little tension made subservient to his special views. In the firstplace, the evidence since adduced not being confirmatory of his diploblasticinterpretation of the sponge embryo, as produced by the delamination ofthe interior from the outer cellular layer, he now declared that essentiallythe same results were obtained, and the same form constructed, by theprocess of invagination. In the second place, the researches, more especially,of Oscar Schmidt, having elicited the fact that in many instancesM 2