98 Introduction to yhiimat Morphology. 



often bears a protective leaf-like appendage (hydro- 

 phyllium), made of a layer of ectoderm, a process of 

 endoderm, and a pouch of the somatic cavity (phyllo- 

 cyst). These may be thin (Diphyes),or thick (Aby la), 

 on the coenosarc, or on the peduncle of the polypite. 

 The gonophores bud from the peduncle, and may be- 

 come planoblastic ; sometimes each carries with it a 

 segment of the coenosarc (which breaks midway be- 

 tween each group), supporting a polypite, tentacle, 

 and hydrophyllium. Such detached parts are called 

 Diphyozooids, and they move by the contraction of 

 the gonocalyx of the medusiform gonophore. The 

 coenosarc grows at the proximal end, so that the oldest 

 polypites are farthest from the somatocyst. 



There are four families : — 



I . Diphyidse — with two polygonal nectocalyces, the hydroe- 

 cium of the proximal being complete ; hydrophyllia large. In 

 Diphyes the proximal nectocalyx is mitrate, pentagonal in trans- 

 verse section, and larger than the distal ; the hydrophyllia are 

 spathiform, smooth ; the diphyozooids are known as Aglaisma, 

 Eudoxia, &c. In Abyla, the proximal nectocalyx is small, 

 polyhedral, the distal large and mitrate ; the hydrophyllia are 

 thick and facetted ; its detached parts are called Diplophysa, 

 Amphiroa, &c. 2. Sphaeronectidse — nectocalyx single, sphe- 

 roidal, with a complete hydroecium ; hydrophyllia none ; tenta- 

 cle attached to the peduncle, ex. Sphaeronectes. 3. Prayidae — 

 nectocalyces two, parallel, with incomplete or groove-like 

 hydroecia ; phyllocyst prolonged into four coecal processes in 

 the thick, reniform, gelatinous hydrophyllia ; male and female 

 medusoids attached to the same ccenosarc, ex. Praya. 

 4. Hippopodidse — nectocalyces many, horse-shoe shaped (Hip- 

 popodium), or many-angled (Vogtia), with incomplete hydroe- 

 cium, and no hydrophyllia. 



Order 2. Physophoridae {Eschscholtz). — Siphono- 

 phora, with the proximal end of the somatic cavity 



