132 SIDNEY F. HAEMER. 



internodes have an odd number of zooeciaj and in which, 

 further, the branch and the basal zooecium are, in each inter- 

 node, on the same side. The third internode which is com- 

 pletely figured has 10 zocEcia, and possesses no branch. It must, 

 however, be pointed out that in his fig. 1 a (C. denticulata, 

 under slight magnification) Milne-Edwards represents most of 

 the internodes as having an even number of zooecia; but it 

 may probably be assumed that in this figure, which gives an 

 excellent representation of the general appearance of the species, 

 sufficient attention has not been paid to the details of the 

 arrangement of the zooecia. Again, Busk^ figures, in the same 

 species, two complete internodes, one of which has thirteen zooecia 

 and a branch, and the next has twelve zooecia and no branch. 



The relations above described are perhaps capable of being, 

 to some extent, explained in the following manner. In the 

 species of Crisia which I have examined, and, I have very 

 little doubt, throughout the genus, the base of an internode, 

 whether axial or lateral, is simply the basal part of the lowest 

 zooecium of that internode, that part having been separated by 

 the development of the joint from its upper or distal part. 

 This will be intelligible on referring to PL XI, fig. 1, repre- 

 senting an axial internode in which only two zooecia are 

 completely separated from the growing-point. The lowest 

 zooecium of the internode is seen to be divided into two parts 

 by the horny joint ; and the lower of these two parts forms the 

 articulation to which the younger internode is attached. In 

 examining the formation of the joint (whether axial or lateral) 

 in stained specimens it is at once obvious that the alimentary 

 canal of the youngest zooecium of the internode at first extends, 

 through the tubular joint, into this lower portion ; confirming 

 the statement made above with regard to the morphology of 

 the base of the internode. 



It is thus clear that the occurrence of an axial joint in 

 no ways disturbs the alternation of the zooecia (see any of 

 the figures). The last zooecium of the older internode would 



' ' Cat. of Mar. Pol. in Brit. Museum,' Part III, " Cyclostomata," pi. iv, 

 fig. 2. 



