httrodiiction to Animal Morphology. loi 



irregular, thick, with a crest formed of ectoderm on the upper 

 :surface ; having a horizontal, long air-sac between its layers, 

 -divided alternately by smaller and larger transverse muscular 

 septa ; the long tentacles have basal sacs, but no lateral 

 branches, and at intervals along their outer wall there are 

 kidney-shaped enlargements, armed with cnidse and an in- 

 ternal muscle-band, ex. Physalia, the Portuguese man-of- 

 war. 7. Vellelidae — with no hydrophyllia nor nectocalyces ; 

 short submarginal tentacles ; a single central polypite below 

 the flattened, strong, chitinous pneumatocyst, which is divided 

 into chambers by concentric partitions, and occupies the 

 whole coenosarc ; the pneumatic cells of the air-sac commu- 

 nicate with each other by openings in the septa, two into 

 each chamber ; there are also external stigmata, six in the 

 vertical plate and about seven in the horizontal ; the soft 

 ectoderm is permeated by ciliated canals ; the hepatic organ 

 is made up of deep brown cells, lining the branchings of the 

 gastrovascular canals, and opening radially (Porpita), or in 

 two series into the stomach (Velella). The genera are : — 

 Velella — oblong, with a solid vertical crest (with oblique 

 surface markings) crossing the disc diagonally ; reproductive 

 zooids planoblastic (Chrysomitra). Porpita — discoidal, with 

 branched tentacles, and no crest ; it has a spongy, guanin- 

 containing body below the pneumatocyst, possibly an ex- 

 ■cretory organ. 



Order 3. Graptolitidae. — Palaeozoic Hydrozoa with a free, 

 •compound, often branched, hydrosoma, and uni- or bilateral 

 hydrothecas containing nematophores, which were probably 

 nutritive ; some had a horny, basal pneumatophore ; other 

 parts are unknown. 



Sub-class 3. Calycozoa [Leiickart^ Podactinaria, 

 M. Edwards) — stalked, oceanic forms, capable of 

 •attachment by an aboral disc (Fig. 13,/). The gene- 

 rative elements lie in symmetrical, band-like pro- 

 jections of the inner surface of the somatic cavity, and 

 are discharged into it. 



There is one order and family, Lucernaridae, which 



