CCELENTERA 863 



prolongations into its cavity (fig. 657) by whose agency (it may be 

 pretty certainly affirmed) the nutrient material is first introduced 

 into the body-substance. This process of ; intracellular digestion ' 

 was first noticed by Professor Allman in the beautiful hydroid polype 

 Mt/riothela ; l the like has been since shown by Mr. Jeffery Parker 

 to be true of the ordinary Hydra ; - and Professor E. Ray Lankester 

 has made the same observation upon the curious little Medusa (Lint/to- 

 codium), which lives in fresh- water tanks in this country, whither 

 it has undoubtedly been introduced ; while the observations of 

 Tvrukeiiberg have shown that a similar process obtains among the sea- 

 anemones. 3 (It may be mentioned in this connection, that Metschni- 

 koff has seen the cells which line the alimentary canal of the lower 

 planarian worms gorging themselves with coloured food-particles, 

 exactly in the manner of Amcefow and the liver-fluke, and that a 

 number of larvre are known to obtain their nourishment in the same 

 way. 4 ) The second ' survival ' of protozoic independence is shown 

 in the extraordinary power possessed by Hydra, Actinia, etc. of 

 reproducing the entire organism from a mere fragment. This great 

 division includes the two principal groups the HYDROZOA and the 

 ACTIXOZOA, the former comprehending the Polypes, and the latter 

 the Anemones. In the Hydrozoa the mouth is placed on a projecting 

 oral cone, while in the Aiithozoa it is sunk below the level of the oral 

 circlet of tentacles, and the cavity developed from and connected 

 with the digestive cavity separates its w r all from the body-wall arid 

 is traversed by a series of vertical partitions or septa. As most of 

 the hydroid polypes are essentially microscopic animals, they need 

 to be described with some minuteness ; whilst in regard to the 

 Actinozoa those points only will be dwelt on which are of special 

 interest to the microscopist. 



Hydrozoa. The type of this group is the Hydra, or fresh-water 

 polype, a very common, inhabitant of pools and ditches, where it is 

 most commonly to be found attached to the leaves or stems of aquatic 

 plants, floating pieces of stick, Arc. Two species are common in this 

 country, the //. virldls or green polype, and the H. vulyaris, which 

 is usually orange-brown, but sometimes yellowish or red (its colour 

 being liable to some variation according to the nature of the food 

 on which it has been subsisting) ; a third less common species, the 

 H.fusca, is distinguished from both the preceding by the length of 

 its tentacles, which in the former are scarcely as long as the body, 

 whilst in the latter they are. when fully extended, many times longer 



Encyclopedia lirit<innir : the ' CliuUenger' licjiorts by Professor Schulze, Messrs. 

 Ridley and Dendy, Polejaeff, and Sollas ; and the numerous memoirs of Professors 

 O. Schmidt and Schulze. More recently important additions to our knowledge of 

 Sponges have been made by Prof. Yves Delage and Monsieur E. Topsent in the 

 Arch. Zool. Exptr. ct (rt'-n. 189-2-5, and by Dr. O. Maas in the Mitth. Zool. Stat. 

 Neapel, x. and elsewhere. 



1 Phil. Trans. 1875, p. 552. It should be noted that the late Professor Claus 

 called attention to the ingestion of foreign bodies by amoeboid cells of Monophyes 

 in 1874. See his Schriften Zool. Inltalts I Wien, 1874!, p. 30. 



- Proc. of Hoy. Soc. vol. xxx. 1880, p. (>1. 



" Quart. Jo//r)i. Mir rase. Sci. n.s. vol. xx. 1880, p. 871. 



4 Consult an interesting article on 'Intercellular Digestion,' by Metschnikoff, in 

 Revue Sclent ifiqiic, ser. iii. vol. xi. p. 683. 



