SUMMARY OF IMPORTANT FACTS 235 



These gonads are regular in distribution, those of two vessels which are 

 nearest each other being of the same sex. The eggs and sperm pass out 

 through the gastrovascular system. 



The few species are divided into TEXT.^CULATA, with tentacles, and 

 NUDA, without. To the first belong the Cydippid^, with pear-shaped bodies 

 (Plciirobrachia'''), Hormiphora (fig. 207); the L0BAT.5: (Mnemiopsis* Bolina*), 

 with lobes; and the band-like Cestid^ (Cestum, Venus girdle). The Beroid^ 

 (Beroe, Idyia*), with wide mouth, belong to the Nuda. The small creeping 

 Ca'loplana and Cteiioplana, are supposed by some to form a transition to the 

 Turbellaria. 



Summary of Important Facts. 



1. The CCELENTERATA and Echinoderma were formerly called 

 Radiata because in most a radial structure is present; in the higher groups 

 this is replaced by biradial or even bilateral symmetry. 



2. The Coelenterata are sometimes called Zoophyta (animal plants), 

 from their appearance and their attachmeirt. In many the resemblance 

 is heightened by their formation of plantTike colonies by fission and 

 budding. 



3. The name Coelenterata was chosen because they have but one 

 cavity, a simple or ramified digestive sac, representing at once the ali- 

 mentary tract and the as yet undifferentiated body cavity. 



4. This coelenteric cavity is called the gastrovascular system because 

 its branches distribute nourishment to all parts and so perform the func- 

 tion of blood vessels. 



5. The reproduction is either sexual or asexual, very frequently 

 cyclical (alternation of generations). 



6. The animals are provided with nerves, muscles, and sense organs 

 and possess marked sensibiHty and mobility. 



7. Especially characteristic are the tentacles and small nettling organs, 

 the cnidte, in special cells. 



8. Nearly all histological differentiation proceeds from ectoderm or 

 entoderm, since the mesoderm (mesoglcea) plays but a subordinate role 

 and usually functions only as a support (Diploblastica) . 



9. Four classes — Hydrozoa, Scyphozoa, Anthozoa, and Ctenophora 

 are recognized. 



10. In Hydrozoa and Scyphozoa there are usually two alternating 

 generations, the sessile asexual polyp and the free-swimming sexual 

 medusa. 



1 1 . The hydroid polyp and the craspedote medusa are characteristic of 

 the Hydrozoa. 



12. The hydroid polyp is a two-layered sac of ectoderm and entoderm, 



