250 Dr. R. von Lendenfeld on Guard-Polyps 
XXX.—On Guard-Polyps and Urticating Cells. 
By Dr. R. von LENDENFELD *. 
I. The Guard- Animals of the Plumularide. 
The Plumularide are ,distinguished, above all other Hy- 
droids, by the fact that a great part, up to five sixths, of all 
the animals of a colony are converted into guard-polyps with- 
out stomachs. Busk Tt was the first who accurately described 
tlre chitinous calices in which the armed animals are seated, 
and directed attention to these structures, which he called 
nematophores. Subsequently Allman} published some ob- 
servations upon the contents of these nematophores, in which 
he sometimes found urticating capsules, sometimes not. He 
states that, leaving out of consideration the urticating capsules, 
the whole contents consist of structureless protoplasm, which 
emits long pseudopodia and retracts them again. Hincks § 
confirms Allman’s statements, and carries the analogy of the 
contents of the nematophores with Rhizopoda still further, 
assuming, like Reichert, for the whole ectoderm of the Hy- 
droida a Bathybius-like ground-mass in which urticating | 
capsules are seated. 
Although F. E. Schultze|/ as long ago as 1872 demonstrated 
the cellular structure of the ectoderm of the Hydroida, it is 
only quite recently, by the researches of Hamann J, that we 
have attained to a more exact insight into the finer structural 
characters of the guard-animals. Hamann explains the con- | 
tents of the nematophore as a modified polyp, for which he 
proposes the designation “‘ machopolyp.” 1 adopt this view, 
and consider that the expression “‘ nematophore”’ should be 
reserved for the chitinous envelope of the guard-polyp. | 
Hamann has demonstrated muscle-cells in the greatly protru- 
sible guard-polyps ; and there is no doubt that the movements 
of the guard-polyp are in part effected by these muscles. I 
say in part, because the parallel fibres, which he in one 
bundle, can only effect the retraction of the guard-polyp, 
while its protrusion is produced by other structures. 
* Translated by W. 8. Dallas, F.L.S., from the ‘ Zeitschrift fiir wis- 
senschaftliche Zoologie, Band xxxviil. pp. 855-370, The author’s third 
communication “ Ueber Coelenteraten der Siidsee.” 
+ Hunterian Lectures, 1857. 
t Ann. & Mag. Nat. Hist. ser. 3, vol. xiii, (1864) p. 203. 
§ British Hydroid Zoophytes, p. xvii (note). 
|| Cordylophora, p. 15. 
§| Jenaische Zeitschrift fiir Naturwissenschaft, Bd. xv. p. 17. 
