410 M, N. Lieberkiihn on the Development of 



more long. The larger are either smooth or furnished with 

 minute spine-like processes. The latter form is also not un- 

 common among the fully developed siliceous needles ; and some 

 Spongillae contain these exclusively. The spicules in the swarm- 

 spores are arranged without definite order. The constant presence 

 of the siliceous needles in the swarm-spores formed the first 

 indication of their origin from the Spougillse. I foimd the 

 swarm-spores both in the broad and in the branched sponge, in 

 that with smooth gemmules as also in those wuth amphidisks. 



Differences in the contents of the Swarm-spores. — These consist 

 principally in the greater or less number of the germ-granules. 

 The mature germ-granules are usually spherical, rarely lenti- 

 cular. Sometimes two of them are relatively so placed, that one 

 extends like a shell over the greater part of the other; such 

 watch-glass-shaped bodies also occur separately, and may also 

 be empty shells. The germ-granules attain the diameter of jg^oy 

 inch, but some of them are much smaller. A very highly refract- 

 ive shell and contents are distinguishable in them. In those 

 occurring in the swarm-spores, the latter are not so distinct as 

 in many of those which are free, and which will be noticed pre- 

 sently. Sometimes they contrast strongly with the shell, and 

 form an ill-defined gelatinous globule ; in many germ-granules 

 they cannot be directly perceived. Notwithstanding their simple 

 form, the germ-granules are so characteristic, that they cannot 

 be mistaken for any other objects. At first sight they might 

 be considered as large fat-globules ; but the difference is soon 

 made manifest when they are strongly compressed and burst. The 

 number of these germ-granules is so great in many swarm-spores, 

 that, with the minute siliceous needles and the albuminous 

 matter, they almost exclusively make up the medullary mass of 

 the swarm-spores ; some being free wdthin it, others aggregated 

 in twos and threes with fatty granules and albuminous matter. 

 These swarm-spores are distinguishable with the naked eye, the 

 highly refractive portion occupying the greater part of their 

 interior, and sometimes forming a perfect spheroid. The above- 

 described form of swarm-spore also appears to contain a white 

 globule, when the anterior part of the spore is directed down- 

 wards and the posterior part upwards; but the real state of 

 things is discovered when it swims in the usual manner. It 

 sometimes happened that one of these aggregations of germ- 

 granules with its siliceous needles escaped completely fi'om the 

 swarm-spore when its envelope was burst by pressure ; it was 

 of a spherical form, and surrounded by a mucoid, structureless, 

 and readily crushed coat. 



The aggregations of germ-granules, of a spherical form, exist 

 free, in vast numbers, in all parts of Spongillse, but especially at 



