CHESTER. — STRUCTURE OF PSEUDOPLEXAURA CRASSA. 757 



of the (.Icxclopinjj; colonics of Authopk-xunni, hut in tlie j,a-o\vin}^ 

 part he founil solenia, which were sometimes continuations of the 

 lon^'ituclinal canals. The .structure of adult Pseudoplexaura supports 

 the conclusion of Kinoshita, that the longitudinal canals have not 

 always developed from inter-mesenterial chambers. 



Structures Concerned in Nutrition. 



Thoufrh I often experimented with small portions of a colony in the 

 laboratory, I saw Aer\' little feeding. Plankton was given, but I saw 

 none of it stunned, and only the smaller less active organisms, such as 

 sea-urchin eggs, were swallowed. Sea-urchin eggs and small pieces 

 of the flesh of fish were placed near the polyps and were often taken 

 into the stomodaeum. Sometimes a polyp kept large pieces of sea- 

 urchin ovary against its mouth for a long time. Usually the whole 

 colony was quite fully expanded, except when it had been vigorously 

 treated. On the reefs colonies with all the polyps contracted were 

 very seldom seen. In the laboratory I could not find any difference 

 in the condition of a colony at night and in the daytime in this respect. 

 Individual expanded polj'ps may have the peristome closed, or polyps 

 that are contracted so that the tentacles are spread out on the coeno- 

 sarc may show it open; but there seems to be no special time for feed- 

 ing. I think the food is undoubtedly from the plankton, and parti- 

 cularly the smaller and more sluggish forms. 



The nettle cells of the smaller kind (Plate 2, Fig. 31, d. nm^cys.'; 

 Plate 4, Fig. 47) are very abundant in the ectoderm of the stomo- 

 daeum, while less numerous on the tentacles. Those of the larger 

 kind (Plate 2, Fig. 26, d. nin'cys.; Plate 4, Figs. 43-46) are most 

 abundant in the coenosarc between the polyps and are seldom 

 found in the tentacles. When sea-urchin eggs are scattered with 

 a pipette over the tip of a branch whose polyps are expanded, they 

 fall slowly, a,nd do not seem to be stopped by tentacle or polyp, 

 but collect in the grooves of the coenosarc. Associated with the falling 

 of sluggish material on the coenosarc, adjacent individual polyps often 

 contract down to the level of the coenosarc with the tentacles still 

 partly spread and the mouth widely open. In such cases the eggs 

 are often draA\'n into the current of the siphonoglyph. The support- 

 ing cells of the stomodaeum have at times small irregular granules 

 at the distal end. These may be zymogen granules or, more probably, 



