RESPAKCHES ON THE DICYEMID^, 135 



the endodermic cell is prolonged. There is prohably no cell- 

 vvall, for the cells are often traversed by embryos wliich are 

 leaving the maternal body, and they readily tnke in foreign 

 substances. The cells of the ectoderm, in the immense 

 majority of cases, contain during their development a num- 

 ber of granules and globules^ which vary in form, size, and 

 refractive power. 



The refractive globules are of two kinds, one perfectly 

 homogeneous and of a spherical or ovoid shape, varying 

 from a size which is scarcely perceptible under tlie highest 

 power of the microscope, to small masses of 003 — 005 mm. 

 in diameter. The other kind are small irregular clots of a 

 granular material. Both descriptions are insoluble in ether 

 and alcohol, are stained first brown and then black by osmic 

 acid, are not coloured either by carmine or hgematoxylin, and 

 give off no gas when treated with acids. Certain " clear 

 droplets " have been noticed in Dicyemopsis macrocephalus , 

 and more rarely in other forms, which are spherical with 

 feeble outlines, and are formed of a homogeneous material 

 which is probably liquid or semi-liquid, and has a gelatinous 

 appearance. They seem to be due to vacuoles in the proto- 

 plasm of the cells. There is still a third element, known as 

 the "refracting rods," which helps to fill the ectodermic 

 cells. These bodies are cylindrical, fusiform, or prismatic, 

 and are scattered through the substance of the protoplasm, 

 or are grouped in a transparent droplet, just as crystals of 

 gtearine are grouped in a drop of fat. These rods may, per- 

 haps, be the deformed heads of spermatozoa belonging to the 

 host. 



The refractive globules are congregated in great numbers 

 in certain cells, so that the surface becomes convex ; here and 

 there true warts (fig. 3, w) are formed, which are most abun- 

 dant in Dicyema typus. In Dicyemina there is a tendency for 

 the refractive globules to accumulate in the two caudal cells ; 

 their nature or function is not known, but that they play no 

 important part in the animal economy is evident from the 

 fact that they vary considerably both in numbers and charac- 

 teristics in different individuals, and may even be entirely 

 absent. 



Each cell of the ectoderm has a flattened oval nucleus, 

 generally situated at its posterior end. When the cell has 

 a wart, such wart is formed by the raising of the central part 

 of the cell (fig. 3), the nucleus being separated from the 

 wart by a membrane with a double contour line, which may 

 be ruptured by strong pressure exerted on the nucleus, which 

 is broken, and the contents, consisting of a semi-liquid, clear 



