hitroducHon to Animal Morphology, 93 



liydranth with proximal and distal rows of filiform tentacles ; 

 planoblasts with one or more simple marginal tentacles, ex. 

 Corymorpha. 18. IMonocaulidae — solitary, naked; hydro- 

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

 caulis. 19. Hybocodonidoe — hydranths as last ; hydrocaulus 

 Avith a perisarc ; planoblasts medusiform, ex. Hybocodon. 

 20. Tubularidae — hydranths with two rows of tentacles ; 

 hydrocaulus with a perisarc ; sporosacs fixed or planoblastic 

 '{Cams); hypostome conical. Some forms periodically shed 

 their hydranths, ex. Tubularia. 21. Hydrolaridse — 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, 

 liaving the periderm expanded at the base of 

 -each hydranth into a cup or receptacle (hydrotheca) ; 

 sometimes with a lid or operculum. The gonophores 

 are at first included in a similar capsule (gonangium), 

 which may hold one gonophore (monomeric), or many 

 on a blastostyle (polymeric). Blastochemes, excep- 

 tional in the last order (Nemopsis), are common here 

 (Campanularidse) ; and sometimes the gonangia are 

 clustered within a common receptacle (corbula). The 

 gonophores may discharge their contents into the sea, 

 or into the cavity of the gonangium, or into a sac at 

 the summit of this cavity, and external to it (acrocyst, 



