RESEARCHES INTO THE DICYEMIDiE. 139 



protoplasm of the germs. When the germs have attained a 

 certain size the protoplasm which separates them contracts 

 and collects round the nucleus of the germ producer, so that 

 the germs themselves are driven to the exterior, though they 

 remain attached to the mother-cell till they have attained 

 their full development. A second, third, and even more 

 generations are in like manner formed and driven out, and 

 thus concentric layers of germs are produced, which are larger 

 as they are further from the centre (fig. 5). 



The infusoriform embryo at the time when it leaves the 

 mother's body to svvim freely in the liquid which bathes the 

 corpus spongiosum of the cuttle-fi.sh is pear shaped, and swims 

 with its larger end, which is known as the head, forwards, 

 whilst the tail, which is conical, is directed backwards. The 

 whole organism is bilaterally symmetrical. The cephalic dila- 

 tation is composed of three organs, one of which is symmetrical 

 and is placed in the middle line, the urn ; the other two are 

 unsymmetrical and lateral, one being placed slightly above 

 and the other slightly below the median organ ; these are 

 known as the refractive and the ciliated bodies (fig. 18), 



The urn (figs. 18 and 19) consists of a margin which is 

 called the capsule of the urn, of a cover which takes part 

 in the formation of the ventral wall of the embryo, and of a 

 contents. The contents of the urn (i) is a cellular body, com- 

 posed of four segments arranged crosswise, each segment 

 being granular, whence the name of the " granular body " 

 which has been applied to them. The function of the urn is 

 not known. 



The refractive bodies (fig. 16 and 18, r) are generally two in 

 number, and are not composed of calcium carbonate, as Kol- 

 liker and AVagener assert. Hgematoxylin prepared with alum 

 causes, them to burst in about three quartersof anhour with an 

 explosion which scatters the refracting globules of which they 

 are composed and projects them to some distance; it is then 

 seen that the bodies were encased in a double wall, one within 

 the other, the inner called the endocyst and the outer the ecto- 

 cyst (fig. 19, ce, ci). The ciliary body is composed of a num- 

 ber of vibratile cells, each of which is conical and contains a 

 spherical nucleus and a sieve-like plate which gives insertion 

 to a number of very long vibratile cilia (fig. 19, c) . The germs 

 of the infusoriform embryos, as was stated above, are pro- 

 duced endogenously, in a cell round which they remain 

 grouped until they have reached maturity. Soon afterwards 

 they undergo the first changes previous to the formation 

 of infusoriform embryos. As development progresses they 

 separate from the germ producer, so that, as a general rule, 



VOL. XVII.— -NEW SER. K 



