248 H. V. Wilson 



This degree of differentiation is attained in the course of six or 

 seven days when the preparations are kept in laboratory aquaria 

 (dishes in which the water is changed answer about as well as 

 running aquaria). Differentiation goes on more rapidly when 

 the preparation is hung in the open harbor in a live-box (a slide 

 preparation inclosed in a coarse wire cage is convenient). Sponges 

 reared in this way have been kept for a couple of weeks. The 

 currents of w^ater passing through them are certainly active and 

 the sponges appear to be healthy. In such a sponge spicules are 

 present, but some of these have unquestionably been carried over 

 from the parent body along with the squeezed out cells. 



The old question of individuality may receive a word here. 

 Microciona is one of that large class of monaxonid sponges which 

 lack definite shape and in which the number of oscula is correlated 

 simply with the size of the mass. While we may look on such a 

 mass from the phylogenetic standpoint as a corm, we speak of it 

 as an individual. Yet it is an individual of which with the stroke 

 of a knife we can make two. Or conversely it is an individual 

 which may be made to fuse with another, the two forming one. 

 To such a mass the ordinary idea of the individual is not applic- 

 able. It is only a mass large or small having the characteristic 

 organs and tissues of the species but in which the shape of the 

 whole and the number of the organs are indefinite. As with the 

 adult so with the lumps of regenerative tissue. They have no 

 definiteness of shape or size, and their structure is only definite 

 in so far as the histological character of the syncytial mass is fixed 

 for the species. A tiny lump may metamorphose into a sponge, 

 or may first fuse with many such lumps, the aggregate also pro- 

 ducing but a single sponge although a larger one. In a word we 

 are not dealing with embryonic bodies of complicated organization 

 but with a reproductive or regenerative tissue which we may start 

 on its upward path of differentiation in almost any desired quan- 

 tity. A striking illustration of this nature of the material is 

 afforded by the following experiment. The tissue in the shape 

 of tiny lumps was poured out in such wise that it formed con- 

 tinuous sheets about one millimeter thick. Such sheets were 

 then cut into pieces, each about one cubic millimeter. These 



