2G2 ME. F. J. COLE ON THE DETELOPMENT OF 



wedged in between the " pseudo-rhabdites " of Nemerteans is a 

 possibility which on]y perfectly preserved material can determine. 

 The three interesting features therefore about the basal cells 

 are: — (1) Their protoplasm is continuous proximally; (2) they are 

 separated by distinct intervals from each other, and present an 

 almost amoeboid appearance: (3) they are connected by one or more 

 nucleated filaments with the periphery of the battery. Lying in 

 the spaces defined by the latter filaments are the rhabdite-" cells " 

 themselves (3) — to be described below. The varying position 

 and structure of these bodies may be noted here. The periphery 

 of the battery is often defined by a fine membrane (i), which 

 seems to rupture to admit the passage of the rliabdites, whilst 

 underlying this is a stratum containing two or three rows of 

 undoubted nuclei (2). What this layer is the condition of the 

 material did not permit me to determine, but many of the nuclei 

 in the particular section shown in the drawing were certainly 

 situated on the filaments described above. It is possible that 

 this layer with its nuclei represents the epidermis, or, together 

 with the basal cells, the dermis. 



Figure 2 shows what I conceive to be an early stage in the 

 development of the rhabdites. The "cell" was projecting 

 slightly from the surface of the battery (1), and contained two 

 highly refractile rounded bodies — one being very much larger 

 than the other. There can be little doubt, from their general 

 appearance and waxy homogeneous structure, that these bodies 

 are simply secretions of some sort, although of what nature 

 I was unable to determine. This identification was at once 

 independently suggested by the biologists to whom I showed 

 the slides. Besides the larger secretions are two smaller aster 

 secretions, which bear a superficial resemblance to centrosomes 

 but which have not of course any relation to those problematical 

 bodies. One of these asters is connected with the smaller 

 secretion-sphere, which suggests that it may have originated by 

 the fragmentation of that body. The asters are also shown in 

 figs. 4, and 6 a & i. Beyond that they appear to pursue the 

 same course of development as the rhabdites themselves, that is 

 to say they are formed by the breaking up of an originally 

 spherical secretion-mass, of which the earliest stage I have seen 

 is shown in fig. 4, I have failed to ascertain where they come 

 from or what ultimate role they fulfil. The presence, however, of 

 other asters consisting simply of very fine rods with no central 



