80 MANUAL OP ZOOLOGY. 



derm of this sac is ciliated, and it is generally so immensely 

 vacuolated as almost to obliterate the internal cavity and give 

 the organ the appearance of a cellular mass.' (Huxley). The 

 polypites in the Ctilycophoridce often show a well-marked divi- 

 sion into three portions, termed respectively the proximal, 

 median, and distal divisions. Of these, the ' proximal ' division 

 is somewhat contracted, and forms a species of peduncle, 

 which often carries appendages. The ' median' portion is the 

 widest, and may be termed the ' gastric division,' as in it the 



Erocess of digestion is carried on. It is usually separated 

 'om the proximal division by a valvular inflexion of the 

 endoderm, which is known as the ' pyloric valve.' The poly- 

 pites have only one tentacle 'developed near their basal or 

 proximal ends, and provided with lateral branches ending in 

 saccular cavities,' and furnished with numerous thread-cells. 

 The proximal ends of the polypites also bear certain over- 

 lapping plates, of a protective nature, which are termed 



* hydrophyllia,' or ' bracts.' They are composed of processes 

 of both ectoderm and endoderm (fig. 19, 3 d), and they always 

 contain a diverticulum from the somatic cavity, which is called 

 a ' phyllocyst.' The Catycophoridce always possess swimming- 

 bells, or 'nectocalyces,' by the contractions of which the 

 hydrosoma is propelled through the water (fig. 19, 2). The 

 nectocalyx in structure is very similar to the 'gonocalyx' of 

 a medusiform gonophore, as already described ; but the former 

 is devoid of the gastric or genital sac the 'manubrium' 

 possessed by the latter. Each nectocalyx consists of a bell- 

 shaped cup, attached by its base to the hydrosoma, and pro- 

 vided with a muscular lining in the interior of its cavity, or 



* nectosac.' There is also always a 'velum,' or 'veil,' in the 

 form of a membrane attached to the mouth of the nectosac 

 round its entire margin, and leaving a central aperture. The 

 peduncle by which the nectocalyx is attached to the hydro- 

 soma conveys a canal from the somatic cavity, which dilates 

 into a ciliated chamber, and gives off at least four radiating 

 canals, which proceed to the circumference of the bell, where 

 they are united by a circular vessel ; the entire system consti- 

 tuting what is known as the system of the ' nectocalycine 

 canals.' In the typical Calycoplioridce two nectocalyces only 

 are present, but in some genera there are more. In Pray a the 

 two nectocalyces are so apposed to one another that a sort of 

 canal is formed by the union of two grooves, one of which 

 exists on the side of each nectocalyx. This chamber, which 

 is present in a more or less complete form in all the genera, is 

 termed the ' hydroecium,' and the ccenosarc can be retracted 

 within it for protection. 



