PLATE 13. 



Ckistatella ophidioidea Hyatt. 



Fig. I. A colony of natural size in its natural position. The polypides 

 are figured at the ends only, the outline of the colony between them being 

 indicated by dotted lines. (Norway, Me.) 



Fig. 2. Enlarged view of the underside of one-half of a young colony 

 with the ectocyst and endocyst removed from a portion of the base, disclos- 

 ing the stomachs of the polypides and the bases of the muscular walls. On 

 the border are the buds attached to the upper side of the endocyst, and in 

 the centre is the inverted cone formed by the interior edges of the muscular 

 walls. On the left, the uncovered portion, the white lines show the posi- 

 tions of the muscular walls, but on the right, the covered portion, they 

 show only the temporary external folds of the endocyst caused by the con- 

 traction of tlie ccencecium. The relations and positions of all these parts 

 are best explained by reference to the ideal section of this colony, as depicted 

 in fig. 3, the lettering being the same in both ; with the exception of K ', 

 stomachs of adult polypides jjartially retracted, andt, stomach of an evagi- 

 nated polypide in fig. 2 ; and D, ectocyst in fig. 3. 



Fig. 3.'* E, endocyst; C, stomach of polypides wholly retracted ; Q, 

 muscular walls ; Y, buds ; Y ', immature polypides, capable of ev agina- 

 tion ;t X, fixed statoblasts ; A ', coenoecial trunk. 



Fig. 4. View from above of a portion of the border of the same col- 

 ony when expanded to about twice the vertical height of fig. 3. Lettering 

 same as in preceding figures, with the exception of A", coencecial tubes, and 

 A "", coenoecial orifices. Some of the latter are closed, and some, indicated 

 l>3 r dotted lines, are open ; the polypides, however, are omitted from the lat- 

 ter, in order to give a better view of the ccencecium. 



Fig. 5. Enlarged coenoecial cell of the first row, the orifice closed 

 over the invaginated polypide. A"", coenoecial orifice; Q, attachments of 

 the muscular walls of the cell; N, anterior retentors. 



Fig. 6. Transverse section of the same, viewed from the ventral side. 

 A "", coenoecial orifice ; Q, muscular walls ; N, anterior retentors ; H, tenta- 

 cles. 



Fig. 7. View of a fully invaginated polypide of the first row, from 

 below, with the endocyst removed from that side. The gastric and part of 

 the lophophoric retractors, have been entirely omitted. A "", coencecial ori- 

 fice ; Q, muscular walls ; M, trunk of retractor muscles ; K ', stomach. 



* When this figure was drawn, I had, as I supposed, observed three rows of full 

 grown polypides on the coencecium as in fig. 2. This, however, is probably errone 

 ou3, and I doubt whether at any lime of the life of the colony, there are more than 

 two living rows of fully grown polypides and one row of immature polypides. In 

 this section, therefore, the innermost rows should have been represented in a re- 

 tracted condition, the polypides dead and partly absorbed. 



t For a magnified view of crest from above, see PI. 9, fig. 14. 



