CHAP. IV 



MESOZOA DICYEMIDAE 



93 



Polyclad Zeptoplana tremellaris. In addition to the undoubted 

 Mesozoa, certain anoma- 

 lous forms Trichoplax 

 adhaerens and Salinella 

 salve may be referred 

 to this group. 



Dicyemidae. If the 

 kidney of Medone ?nos- 

 chata, a Cephalopod 

 common on our south- 

 western shores, be opened, 

 a number of fine, yellowish, 

 hair -like filaments may 

 be seen attached at one 

 end to its inner surface, 

 floating in the fluid con- 

 tained in the renal cavity. 

 These may be Dicye- 

 mennea eledones Wag., 

 although another form, 

 Dicyema moschatum 

 Whit., also occurs in the 

 same host. D. eledones 

 (Fig. 46) is 7 to 9 mm. 

 long, transparent, and is 

 composed of one large 

 inner cell with a simple 

 nucleus (Fig. 46, n.end), 

 and of an outer layer of 

 ciliated cells, nine of 

 which form the " cal- 

 otte " or pole by which 

 the animal is attached. 

 Within the former (en- 

 dodermal) cell the for- 

 mation of urn -shaped 

 " infusoriform embryos " 

 takes place (B and C), 

 the fate of which is not known, but they are possibly the males. 

 The individual which produces these larvae is called a " Ehom- 



F IG . 46. Dicyemennea eledones Wag., from the 

 kidney of Medone moschata. A, Full-grown 

 Rhombogen with infusoriform embryos (emb) ; B, 

 one of the latter developing ; C, fully formed ; 

 D, calotte, composed of the upper nine cells 

 shown in the figure. (After Ed. van Beneden and 

 Whitman.) emb, Infusoriform embryo ; g, part of 

 endoderm-cell where formation of these embryos is 

 rapidly proceeding ; n.ect, nucleus of ectoderm- 

 cell ; n.end, nucleus of endoderm-cell ; p, "calotte." 



