Introduction to Animal Morphology. 93 



hydranth with proximal and distal rows of filiform tentacles ; 

 planoblasts with one or more simple marginal tentacles, ex. 

 Corymorpha. 18. Monocaulidse solitary, naked; hydro- 

 caulus with hydranths, as last, and fixed sporosacs, ex. Mono- 

 caulis. 19. Hybocodonidoe hydranths as last ; hydrocaulus 

 with a perisarc ; planoblasts medusiform, ex. Hybocodon. 

 20. Tubularidae hydranths with two rows of tentacles ; 

 hydrocaulus with a perisarc ; sporosacs fixed or planoblastic 

 (Carus); hypostome conical. Some forms periodically shed 

 their hydranths, ex. Tubularia. 21. Hydrolaridce hydro- 

 caulus undeveloped ; hydranths with two filiform tentacles 

 from one side of the base of the bilabiate hypostome, which 

 has a head-like lobe ; planoblasts with six radial canals and 

 simple marginal tentacles. The trophosome of Lar is very 

 singular in form. 



CHAPTER XIV. 



HYDROZOA. 



ORDER 3. Calyptoblastea (Allman}. Colonial forms, 

 having the periderm expanded at the base of 



h hydranth into a cup or receptacle (hydrotheca) ; 

 \vith a lid or operculum. The gonophores 



at first included in a similar capsule (gonangium), 

 which may hold one gonophore (monomeric), or many 

 on a blastostyle I'polymeHc . Blastochemes, excep- 

 tional in th- rder \Vmnp.sis), are common hen- 



:n]>anulari<he ; and sometimes the gnnangia are 



clustered within a common receptacle em-hula, i 



may di utents into the sea, 



or into tin- cavity of tl.' :i^ium, or into a sac at 



^ummit of this cavity, and external t<> it(acrocyst, 



