396 Miscellaneous. 



from a number of observations on various animals, I have been led 

 to the conclusion that all vibratile cilia originate in the ainorpJinvs 

 intercellular substance. In no instance have I ever seen vibratile 

 cilia forming direct })rolongations of cells, but invariably I find their 

 bases imbedded in the intercellular cytoblastema. They may seem 

 to be prolonged from the underlying cells ; but, on the contrary, as 

 I have ])articularly satisfied myself in regard to the branchioe of the 

 oyster {Ostrea virginiana), they are based in the cytoblastema, 

 which extends in a thin stratum over the outer ends of the cells. In 

 other instances they alternate with the cells, projecting in rows be- 

 tween them, and forming, as it were, a bristling corona to each cell, 

 as I have seen in the ei)ithelium of the intestine of the young Snap- 

 ping Turtle (Clichjilra serjientina). In the latter instance, when the 

 cells are loosed from the intestine, they carry the overlying cyto- 

 blastema with them, and consequently, also, the vibratile cilia, which 

 then falsely appear like ajjpendages of the cells themselves. The 

 nettling cells {cnida) of Polypi and Acalephse originate in the same 

 substance (the intercellular cytoblastema) as do vibratile cilia. 

 They have been supposed to develope within the cells of the layer in 

 which they are situated ; but this is not true. Oftentimes, when 

 cnidse are removed from their basis by pressure, they drag along 

 with them a portion of the cytoblastema, which encloses them like 

 a transparent envelope, and has the appearance of a cell. Sometimes 

 three or four cnidse are pressed out together, and, being covered by 

 the accompanying cytoblastema, they present the deceptive appear- 

 ance of several cnidae in one cell. 



There are four periods in the history of cnidse. Wagner (Wiegm. 

 Archiv, 1835) was the first to detect the existence of these bodies ; 

 but he mistook them for peculiar forms of spermatozoa of Actinia 

 Cereus). Immediately after this, if not at the same date, Ehrenberg 

 (Abhandl. Berlin Akad. 183."), Jahrg. [1837] p. 147) recognized 

 their true office, and described them as the prehensile organs 

 (Fangangeln) of Hydra. Yet in 1842 (Wiegm. Archiv) we find 

 him inclined to deny that they have stinging properties, such as 

 Wagner attributes to those which he found in Pelagia noctiluca. 

 In 1841 (Wiegm. Archiv, p. 38) Wagner described the nettling- 

 organs (Nesselorgane) of Pelagia noctiluca; and although he detected 

 the spirally-rolled thread in the capsule, and says of the thread, 

 "sometimes it appears as if it had a canal," and figures it so in his 

 •Icones Zootomicse' (1841, pL 33. fig. 9 b), yet it was reserved for 

 Doyere, in the latter part of the next year (Comptes Rendus, Aug. 

 1842, p. 429, "Note sur quelques points de I'Anatomie des Hydres 

 d'Eau douce "), to describe the mechanism of the cnidae, and the 

 mode of evolution of the thread, with such completeness as to anti- 

 cipate everything in this regard that has been published since, up to 

 the year 1860, when I figured and briefly pointed out (in Agassiz's 

 'Contributions,' vol. iii. pi. 1 1''. fig. IG'*, Aurelia Jlavidula, and de- 

 scription of plate, p. 1 7, and pi. 1 1^ fig.,5, Coryne mirabilis) an as yet 

 undescribed relation of the thread to the cell in which it is coiled up. 

 As the brilUant discovery of Doyere has been kept in comparative 

 obscurity, at least in America, I will quote from his paper such 



