DEVELOPMENT OF SPONGES FROM DISSOCIATED TISSUE CELLS. 5 



Structure of large branched specimen. — Comparison makes it obvious that large branched specimens, 

 like that shown in figure i, arise through continued growth and anastomosis of lobular outgrowths of 

 younger specimens. Any part of such a sponge therefore repeats the structureof one of these outgrowths, 

 although there are details of structure in which the older sponges differ from the yoimg. Thus the 

 spiculo-fibers in the former are much thicker than in the latter. The megasclc-res. too, are thicker, and 

 the small echinating styles are abimdant. The larger megascleres may be i2-i6h thick and the head 

 end minutely spinulate. The echinating styles are chiefly spinose and about 8o;i long, but smooth 

 ones sometimes larger are also present. Microscleres, which are only scantily present, include isochelge 

 i2-i6« long, and toxas i6-40/( long. 



MicTociona prolifera Verrill and Smith. Report on the invertebrate animals of Vineyard Sound. Report U. S. Fish Commission 

 1871-72. p. 447, 1874. H. V. Wilson, Sponges collected in Porto Rico in 1899, Bulletin U, S. Fish Commission, vol. xx, 

 1900, pt. I, p. 396, 1902. 



METHOD OF OBTAINING DISSOCIATED CELLS, FUSION OF CELLS, AND FORMATION OF 



PLASMODIA. 



A branched specimen of Microciona in good condition is cut with scissors into pieces 

 about one-fourth inch in diameter. The pieces are then strained through fine bolting 

 cloth, such as is used for tow nets. A square piece of cloth is folded like a bag around the 

 bits of sponge and is immersed in a saucer of filtered sea water. While the bag is kept 

 closed with the fingers of one hand it is repeatedly squeezed between the arms of a small 

 pair of forceps. The pressure and the elastic recoil of the skeleton break up the living 

 tissue of the sponge into its constituent cells, and these pass out through the pores of the 

 cloth into the surrounding water. The cells streaming out through the cloth present 

 the appearance of red clouds. They quickly settle down on the bottom of the dish like 

 a fine sediment. By using the branched specimens of Microciona large quantities of this 

 "sediment" may be had. The lobes of incrusting specimens or even the sheet-like 

 body of such specimens may be cut up and used, but naturally the dissociated cells are 

 obtained in comparatively small quantity. 



If a drop of the "sediment " so obtained be examined at once on a slide with a high 

 power the preparation is seen to consist of myriads of separate cells together with a 

 few spicules. There is a certain resemblance to a blood preparation, which at once sug- 

 gests itself, sea water occupying the place of the plasma. The cells (fig. 21, pi. iv) 

 fall into several classes. The most conspicuous and abundant are spheroidal, densely 

 granular, reddish bodies about 8/( in diameter. These cells are obviously the unspecial- 

 ized ama-boid cells of the sponge parenchyma (amabocytcs). They put out hyaline 

 pseudopodia that are sometimes elongated, more often rounded and blunt. There is 

 also a great abundance of partially transformed collar cells, each consisting of an elon- 

 gated body with slender fliagellum. The cell body is about 8/( long, hyaline, and without 

 a collar, the latter doubtless having been retracted. The flagellar end is thick and 

 rounded, and contains the nucleus, the body tapering away to a point at the opposite 

 end. The flagella are long and hyaline, and at first are vibratile, the cells moving about. 

 Soon however the flagella cease to vibrate. The third class of cells is not homogeneous. 

 In it I include more or less spheroidal cells ranging from the size of the granular cells 

 down to much smaller ones. Many of these are completely hyaline, while others consist 

 of hyaline protoplasm containing one or a few granules. 



