PLATE 8. 

 PLUMATELLA ARETHUSA Hyatt. 



Fig. 1. General view of one colony, life size, with most of the poly- 

 pides retracted. (Norway, Me.) Three apertures in the ectocyst of the 

 main trunk indicate the former positions of as many living poiypides, and 

 show this colony to have been a branch of a much larger colony, from 

 which it has been separated by the death and disappearance of the original 

 stock. 



Fig. 2. One polypide evaginated, with a younger polypide from the 

 same cell invaginated. D, ectocyst, E, endocyst ; Y, bud ; M, gastric re- 

 tractors ; M ', lophophoric retractors ; M ", brachial retractors ; M, trunks of 

 the retractors. F, brachial collar; V, funiculus; W, statoblasts ; W", 

 gelatinous envelope ; N, anterior retentors ; N ', posterior retentors ; A "", 

 coenoecial orifice ; L, region of the sphincter. 



Fig. 4. View of the cceno3cial orifice of fig. 2, from above, showing 

 the four broad plications of the invaginated fold. The crenulations on the 

 border are produced by the contraction of the sphincter, and do not indi- 

 cate cellular structure. 



Fig. 5. Special view, showing the arrangement of the retentor mus- 

 cles around the invaginated fold of the evaginated zooid in fig. 2. The five 

 anterior rows of the posterior retentors are contracted, and have drawn the 

 external wall into five slightly crenulated folds. N, anterior retentors ; N ' 

 posterior retentors ; L, region of the sphincter. 



Fig. 6. View of the partial division between the cell of fig. 2 and 

 the preceding poiypides, formed by an infolding and thickening of the endo- 

 cyst. D, ectocyst ; E, endocyst. 



Figs. 7, 8, 9. Upper and lower sides and profile view of the statoblast. 

 W ', horny sheath ; VV ", annular sheath ; W "", gelatinous envelope. 



Fig. 10. View of a dead and half decayed specimen, showing the pe- 

 culiar constrictions of the cell occasioned by annular muscular bands. D, 

 ectocyst ; E, endocyst ; H, tentacles ; I", mouth ; L, region of the sphinc- 

 ter ; K ', stomach ; M, trunk of the retractors. 



PLUMATELLA DIFFUSA Leidy. 



Fig. 11. An old colony of life size, with but few living poiypides. 

 (Cambridge, Mass.) 



Fig. 12. Enlarged lateral view of a branch from a younger colony, 

 showing different degrees of invagination. First cell on the left has even 

 the upper pliable part of the ectocyst drawn in ; second cell is vacant, the 

 polypide and softer parts having entirely decayed; third, fourth and 

 sixth cells show different degrees of invagination. 



Fig. 13. Enlarged view of another variety of this species with all the 

 poiypides retracted. 



Fig. 14. Enlarged Ten tral view of the expanded crest of a polypide 

 from fig. 13. M', lophophoric retractor; M", brachial retractors. 



