POLYCECA. 



[ 621 ] 



POLYPI. 



in its habits, swimming by means of its 

 wings. It lays its eggs inside those of 

 Dragonflies. 



BIBL. Lubbock, Linn. Tr. 1863 j Metam. 

 Insect. 37. 



POLYCE'CA, Kt A. genus of Choano- 

 flagellate Infusoria. Like Salpinyceca, but 

 the carapaces united into a branched zoary. 

 P. dichotoma, marine. (Kent, Inf. 360.) 



POLYOM'MATIJS, Latr. A genus of 

 Lepidopterous Insects, of the family Lycae- 

 nidae. 



Char. Antennae terminated by a con- 

 tracted knob ; tarsal claws minute ; wings 

 not tailed. 



The (thirteen) species are small butter- 

 flies, the upper surface of the wings of a 

 beautiful blue colour, the under side grey 

 or brownish, and with numerous eye-like 

 spots. 



The scales upon the under surface of the 

 wings of P. argiolus and P. argus have 

 been proposed as test-objects. They are of 

 two kinds one resembling in structure the 

 ordinary scales of insects, the other of a 

 battledore form (PI. 34. figs. 20 & 21). See 

 SCALES of INSECTS and TEST-OBJECTS. 



The species are figured in Westwood's 

 British Butterflies. 



POLY^PHE'MUS, Mull. A genus of 

 Cladocerous Entomostraca, family Poly- 

 phemidae. 



Char. Head distinct from the body ; ab- 

 domen long, slender, and projecting exter- 

 nally from the shell. 



P. pediculus (PI. 19. fig. 29). The only 

 species. Freshwater. 



BIBL. Baird, Brit. Entomostr. Ill ; An. 

 N. H. 1877, xix. 119 ; Claus, Polyph. 1877. 

 POLYPHRAG'MA, Reuss. A. large 

 stichostegian Arenaceous LitKola, with nu- 

 merous short chambers and cribrate septa. 

 Fossil ; Cretaceous. Saxony and Bohemia. 

 BIBL. Von Reuss, Geinit^s Elbthalgebirge, 

 I. iv. 139. 



POLYPI. A group of Zoophytes, com- 

 prising the Actinaria and Hydroida. Body 

 rounded or cylindrical, with a distinct 

 rnouth, surrounded by retractile non-ciliated 

 tentacles or radiating lobes: individuals 

 usually aggregate; gemmiparous and ovi- 

 parous. 



The polypes are usually enveloped in an 

 external (PI. 41. figs. 46, 12, & 14), or 

 supported by an internal axial skeleton 

 (PL 41. fig. 6), called the polypidom. This 

 is either horny, leathery, or calcareous. 

 Most polypes are united into smaller or 



larger groups by the polypidom, which 

 often possesses an elegant plant-like form 

 (PL 41. fig. 15). The tubular or cup- 

 shaped processes or cavities in which the 

 body of the individual polypes is contained, 

 form the polype-cells or capsules ; they are 

 sometimes furnished with a kind of lid. 



The structure of the calcareous polypi- 

 dom s has not been satisfactorily deter- 

 mined. They are usually traversed by vas- 

 cular canals, and appear in some cases at 

 least to consist of aggregated and fused 

 spicula. 



The polypes are rarely free, or capable of 

 fixing themselves by a disk at the base of 

 the body, as in Hydra, being usually fixed 

 at the bottom of the polype-cells, the poly- 

 pidoms being attached by a rooting base to 

 some foreign body. Imbedded in the outer 

 parts of the soft substance of the body, 

 especially the tentacles, are stinging organs 

 (PL 41. fig. 22), resembling in general those 

 of the Acalephae. 



In many, distinct muscles are present ; 

 but the fibres are not transversely striated, 

 although frequently exhibiting wrinkles. In 

 some polypes, the substance of the body 

 consists entirely of sarcodic substance. In 

 many, both the integument and the sub- 

 stance of the body contain calcareous spi- 

 cula (PL 41. figs. 7, 27, & 28). 



The alimentary apparatus consists of a 

 mouth and a simple gastric sac, the food 

 being admitted and the undigested portion 

 rejected from the single aperture, except in 

 one genus, where the anus is separate. The 

 oral orifice is usually surrounded by a ring 

 of contractile arms and tentacles, which are 

 hollow internally, and communicate with 

 the cavity of the abdomen ; sometimes the 

 tentacles are distributed over the surface of 

 the body. 



The simple gastric cavity is usually sepa- 

 rated from the cavity of the body j where- 

 by a larger or smaller abdominal cavity is 

 formed, which is usually prolonged into 

 the hollow arms, and in many polypes 

 living in colonies passes into the canals 

 traversing the interior of the polypidom, so 

 that the abdominal cavities of the indi- 

 vidual polypes are all brought into con- 

 nection by these canals. Sometimes longi- 

 tudinal partitions run like a mesentery 

 from the outer to the inner surface of the 

 abdominal walls, thus dividing the abdo- 

 minal cavity into chambers. The bottom 

 of the gastric cavity is provided with one 

 or more spontaneously closeable openings, 



