On the Nematocysts of AEolids . not only that the immunity is by no meanscomplete, but also that it depends on something besides a copioussecretion of mucus. 2. The presence of only undischarged nematocysts in the cnidosacsof Solids may be due to the nematocysts never having been discharged,or to the threads of discharged nematocysts having re-inverted by theaction of the digestive fluids. When a hydroid polyp is plucked off and examined in sea water the 1903.] On the Nematocysts of jEolids. 481 small nematocysts of the tentacles usually remain undischarged; even thelarge nematocysts found at
On the Nematocysts of AEolids . not only that the immunity is by no meanscomplete, but also that it depends on something besides a copioussecretion of mucus. 2. The presence of only undischarged nematocysts in the cnidosacsof Solids may be due to the nematocysts never having been discharged,or to the threads of discharged nematocysts having re-inverted by theaction of the digestive fluids. When a hydroid polyp is plucked off and examined in sea water the 1903.] On the Nematocysts of jEolids. 481 small nematocysts of the tentacles usually remain undischarged; even thelarge nematocysts found at the base of the tentacles of many hydroids(Eudendrium) are often not discharged unless the polyps are teasedupj compressed or otherwise stimulated. It is quite possible, therefore,that no attempt is made by the prey to discharge its nematocysts tillit has been swallowed by the ^olid and immersed in juices of sufficientconcentration to prevent the discharge. Perhaps a preliminary coveringof mucus may help to delay the On the other hand, since it is known that the thread of a developingnematooyst is formed outside the capsule and is only inverted whencomplete, presumably by the extraction of water from the capsuleby the surrounding protoplasm, it is quite possible that the gastricjuices of an ^olid may have the same effect on a discharged nema-tocyst. Development and Structure of the Gnidocysts. Thanks to Davenport, Hecht and Krembzow, the origin of thecnidosacs from the distal extremities of the ceratal diverticula of thegastric gland is thoroughly established, and the general outline of itsdevelopment known. What observations, however, have been made on 482 Mr. G. H. Grosvenor. [Kov. 3, the structure and development of the individual cnidocysts have, ofcourse, been from the generally accepted point of view^ ^ that theyare nematocyst-secreting cells, instead of receptacles for fully formedforeign nematocysts. The embryonic tissue of the cnidosac lies at the base,
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