174 



hand it is suggestive that the nematocysts become more numerous about 

 the mouth. There is no trace of siphonoglyphes. 



The pharynx extends inward for a distance equal to one seventh 

 the length of the body, and its walls throughout are developed into pro- 

 minent folds, which in a general way correspond to the septa and so 

 are disposed symmetrically. In the neighborhood of the mouth the 

 pharyngeal cavity presents an irregular quadrilateral form, but more in- 

 wardly and especially near its junction with the gastrovascular cavity 

 it assumes more the appearance of a transverse slit. While its walls are 

 of varying thickness, especially in the lateral folds the cells are of essen- 

 tially the same character. The more abundant are comparativly long 

 and slender with the nucleus holding a position about the middle of the 

 cell, whose basal half is much vacuolated. These cells bear a moderately 

 heavy coat of cilia. But slightly less numerous are gland cells, of a very 

 slender vase shape, the glandular secretion staining activly with haema- 

 toxylin. Gland cells belonging to another distinct class and more in- 

 frequent, especially in the neighborhood of the oral opening, also occur 

 in the pharyngeal lining. They are of a more decided vase shape and 

 the secretion is coursely granular, and in color closely resembles the 

 pigment of the ectoderm. Finally nematocysts , of about the same size 

 and shape as the larger type occurring in the ectoderm, are jDresent in 

 the deeper portions of the pharyngeal epithelium. They are relativly 

 infrequent, not more than one or two appearing in the same section. 



The mesogloea is relativly thick, almost totally unaffected by Delà - 

 fields haematoxylin and appears to be homogeneous or slightly fibrous 

 under high magnification. In Z. lienseni^ acccording to van Ben e den 

 it contains numbers of cells of two distinct classes, but in Z. galapagoen- 

 sis all are of essentially the same character. Here and there are elements 

 somewhat larger than usual but it is probable that they are the result 

 of the contraction of the ordinary cells, which are usually spindle shaped, 

 rarely stellate and at many points extend across the mesogloea. Cells 

 of this same general shape are also closely applied to the ectoderm or 

 endoderm where they may form a fairly distinct though probably tem- 

 porary layer. 



The coelenteron, septa and endodermhave been accurately described 

 in the case of Z. henseni, and the description answers so closely for the 

 present species that a detailed account is unnecessary. In both species 

 twelve septa are present, six macrosepta and six microsepta alternating 

 with each other, and arranged symmetrically with reference to the 

 dorso-ventral plane. The macrosepta alone unite with the jiharynx and 

 extend nearly to the aboral pole of the animal. The free border of each 

 terminates in a mesenterial filiment, which at this stage shows no ten- 



