Martin, A Note on the Occurrence of Nematocysts and Similar Structures etc. 255 



described in the sections of the proboscis, the prolongation of the 

 tentacles as separate tubes down the proboscis. The first stage in 

 feeding is shown in PI. 15, figs. 1 and 2, in which one nematoblast 

 has been pulled out of its position in the ectoderm of the hydroid, 

 the later stage is shown in a drawing from a living specimen, text- 

 fig. 3, and from a stained preparation PI. 15, fig. 3. It would seem 

 that the size of the nematoblasts prevents their passage down 

 the tentacles as long as the proboscis is in its fully extended 

 condition. 



After passing down the proboscis the ingested ectodermal cells 

 may be found (PI. 15, fig. 3) lying in the cytoplasm of the Ophryoden- 

 dron, and in some cases the whole body is absolutely blocked by 

 them. The cytoplasm of these cells seems to undergo fairly rapid 

 digestion, but the nucleus is far more resistant; in early stages 

 the nucleus retains its characteristic shield-shape and vacuolar 

 appearance, but under the influence of the digestive enzyme its 

 structure breaks down, and finally the only trace left of it is a 

 number of dots of darkly staining matter lying in 

 small vacuoles dotted through the cytoplasm of the 

 animal." 



In all these cases of the presence of Clepto- 

 cnids in Protozoa, there is no evidence that these 

 structures are of any value to llie animals that 

 contain them, and in this point these cases differ 

 from the Cleptocnid in Turbellaria and Aeolids which 

 are described below. jj a jj^ 



There is one further case of the occurrence of 



Nematocysts in the group of Protozoa which I am inclined to place 

 in this category, and that is the occurrence of Nematocysts in 

 the Dinoflagellate Polykrikos. I have unfortunately never been 

 able to obtain an example of this animal, and therefore it is 

 impossible for me to arrive at a definite conclusion of this question. 



These structures are fully described by Biitschli in his work 

 on Protozoa , Band I, p. 970, 



,,Zu den merkwiirdigsten Erzeugnissen des Plasmas einer Dino- 

 flagellatenform gehoren die Nesselkapseln und sind in vieler Hin- 

 sicht beachtenswert. Einmal, weil sie unter den zurzeit bekannten 

 Formen ganz unvermittelt bei der einzigen Gattung Polykrikos 

 auftreten und weil sie viel holier entwickelt sind als bei sonstigen 

 Protozoen. Wohl begegnet man ja bei Flagellaten und Ciliaten 

 nicht selten den in mancher Hinsicht nesselkapselartigen Tricho- 

 cysten, nur bei einer einzigen Ciliatenform aber (Epixtijlis flarictut*) 

 wurden echte Nesselkapseln beobachtet, die wir unter den Proto- 

 zoen sonst nur nodi bei den Myxosporidien finden. Doch ist die 

 Ausbildung der Kapseln in den letztgenannten Fallen eine viel ein- 



17* 



