12 AKT. 5. N. YATSU I 



In young Lingula, or near the tip of the branches of the 

 palliai sinus in the adult, the epithelial ridge is composed of tall 

 columnar cells with enlarged tips and narrowed bases, showing 

 no difference from the structure described by Blochmann foo). 

 In older individuals, however, this region gives quite a different 

 aspect. In sections of the mantle cut perpendicular to the 

 epithelial ridge (PI. L, Figs. 5, 9, 10), the following relations will 

 best be seen. The boundary between the tall columnar cells 

 forming the epithelial ridge vanishes as if the cells had been 

 disorganized to a certain extent. The nuclei placed in the lateral 

 portion of the ridge point away from the middle line of the 

 latter. Near the base of the ridge there are found yellowish 

 brown pigment granules. A number of the spindle bodies occur 

 imbedded in the epithelial ridge, and, in a majority of cases 

 lie in a cavity which has no membrane delemiting it from the 

 neighboring part. What attracts special attention is the fact that 

 the spindle bodies are found lying in any position in the ridge : 

 sometimes they stand almost perpendicular to the surface, while 

 in other cases they are placed nearly parallel. In an extreme 

 case the spindle body is so elongated that its length exceeds the 

 thickness of the ridge and appears to find hardly room enough 

 for itself there (PI. I., Fig. 11). From these facts alone one 

 may consider that the spindle bodies do not belong to the epi- 

 thelial ridge, but that they are introduced fronr without. That 

 the spindle bodies, or at least their antecedents, are thus in- 

 troduced will be shown directly. When they attain full growth 

 they are set free into the palliai sinus. And very often there 

 are seen holes which are formed after the escape of the spindle 

 bodies. The sections through the middle line of the epithelial 

 ridge also give very instructive figures, spindle bodies of dif- 



