384 Mr. H. J. Carter on the Nutritive and 



the remaining projection of the still waving tail, such as those 

 in Keller's instance, is confirmative of impregnation, simply 

 because, when these polymorphic bodies become amalgamated, 

 their water-like sarcode so flows together that their individu- 

 ality becomes lost — although, where the body is not a sperma- 

 tozoon, they can immediately individualize themselves again. 

 Nothing is more like the " melting away" of a spermato- 

 zoon when it passes into the ovum than the union of two 

 polymorphic amoeboid Infusoria ; so, unless the act itself is 

 seen (that is, the spermatozoid and ovum are both observed 

 before union), the case may only remain " probable," as 

 Keller has observed. 



Gemmule or Seed-like Body o/Spongilla. 

 Turning our attention shortly to the seed-like body of 

 Spongilla for our present purpose, as I have already given this 

 in detail (no. 12), we find that it is more or less globular in 

 form according to the species, variable in size, although 

 generally nearly as large as a small pin-head, so that they can 

 be easily seen by the unassisted eye, congregated towards 

 the base or first-formed parts of the Spongilla, consisting of 

 a cellular crust more or less charged with peculiar spicules, 

 lined by a coriaceous membrane, and filled with a yellowish 

 substance, something like the yelk of a hard-boiled egg f 

 which is composed of transparent spherical sacs varying 

 under l-1000th inch in diameter, more or less filled with 

 grain-like transparent compressed firm cells of different 

 sizes varying under 1 -3000th inch in diameter, bearing in 

 one part of the crust a hilous aperture, through which the 

 contents issue a few days after the seed-like body has been 

 placed in water, in the form of the young Spongilla (no. 3, 

 p. 87, pi. iii. fig. 6, a-i). 



If this growth be made to take place in a watchglass under 

 cover of a bell-glass, or something of the kind, replenishing 

 the water as required, it can easily be transferred to the field 

 of a microscope from time to time, where it can be viewed 

 under ±-inch object-glass, of course immersed ; when the 

 "transparent spherical sacs" with their "grain-like cells" 

 appear to issue entire with the rest of the substance from the 

 seed-like body, and so become developed in their entirety, 

 respectively, in this substance, now assuming the form of a 

 parenchyma (no. 6, pp. 21, 22). 



On the other hand, the development of the swarm-spore or 

 embryo leads to the same result, when some of its cell-contents 

 also become developed into ampullaceous sacs (no. 13, p. 337, 

 pi. xxi. fig. 21, c, &c, and pi. xxii. fig. 34, d), 



