266 MR. r. J. COLE ON the deyelopmekt oe 



Stabchenzellen des lebenden Thieres leieht iiberzeugen kann." 

 The " Flimmerhaaren " I have not seen in Cephalodiscus, although 

 it is possible that living material may disclose them. Lang's 

 account of the development of the rhabdites is too ]ong to be 

 quoted in extenso, but may be summarized as follows : — Situated in 

 between the mature rhabdite-cellshere and there are much smaller 

 cells each containing a nucleus. Lying close to the nucleus is 

 a single small, round, homogeneous, highly refraetile body. This 

 body Lang regards as essentially a secretion. It grows and frag- 

 ments to form a number of small balls, and each ball becoming 

 lengthened and spindle-shaped, forms a rhabdite-rod — the wliole 

 of the rods becoming subsequently arranged to form a pyramidal 

 bundle with the base opposed to the nucleus. Tlie rhabdite- 

 cells therefore contain a nucleus, plasma, and the rods. Lang 

 and Graff are agreed that they are gland-cells, and that the 

 rhabdites are their secretion. 



The Pseudo-rhabdites of Lang have an uneven periphery. 

 They are figured in some species as one or more tall columns of 

 end to end secretion-fragments (Block ch en) ofan irregular shape, 

 with the nucleus and plasma of the cell lying at its base and under 

 the pseudo-rhabdites. In Stylochus, Lang says (pp. 53-54) : — 

 " Die einzelneu Blockchen entsprechen ihrem optischen Yer- 

 halten nach sehr den Ehabditen, sie sind klar, homogen, stark 

 lichtbrechend und verhalten sich Parbmitteln gegeniiber ganz 

 wie diese. Die Saulen, die sie bilden, erfiillen beinahe die ganze 

 Epithelzelle, in der sie liegen, und lassen hochstens am basalen 

 Theil, wo der Kern liegt, ein Kliimpchen feinkornigen Plasmas 

 frei." Lang considers that the pseudo-rhabdites are fully com- 

 parable to the true rhabdites, and describes several stages 

 intermediate between the StylocJius-tyipe and the mature rhabdite- 

 cell with its clump of rods. 



Just as the pseudo-rhabdite must be regarded as a compara- 

 tively simple modification, in which the secretion has not under- 

 gone such differentiation as in the true rhabdite-cell, so do 

 certain gland-cells in Nemertea represent a condition antecedent 

 to the pseudo-rhabdite form. Hubrecht * describes and figures in 

 Gerehratulus and Eupolia unicellular glands which he considers 

 correspond precisely to the pseudo-rhabdites of Lang. They have 

 in Gerehratulus highly refraetile uniform contents, not^ however^ 



* ' Challenger' Eeports, vol. xix. p. 61. 



