SCIPIIOMEDUS.i: CALYCOZOA* 



257 



t'i) Sub-order: Calycozoa (Cylicozoa). 



Cup-shaped Acalepha attached by their aboral pole. They have 

 four wide vascular pouches separated by narrow walls, and eiyht arm- 

 Uke processes beset with tentacles on the edge of the umbrella. 



The Calycozoa are best considered in their relation to the Scyhis- 

 toma. They may be looked upon as Seyphistoma deprived of 

 their tentacles, which indeed are only transitory structures, and 

 elongated so as to assume the form of a cup, and changed in 

 several particulars which are characteristic of the medusa stage. 

 The four septa arise by the fusion of the four gastric folds with 

 the wide oral disc, which becomes drawn in and concave like a sub- 

 umbrella. These four septa separate the same number of gas- 



FIG. 197. a, A Calycozoon (Luccrnar'a) from the oral surface magnified about 8 diameters. 

 S, Septa of the four gastric pouches ; L, longitudinal muscle fibres with the genital band ; 

 Hi, marginal tentacles, b, The Calycozoon seen from the Bide ; G, Genital organs ; Gm, 

 gastric fold in the stalk ; at the base ia the foot gland. 



trovascular pouches ; while the margin of the cup is drawn out into 

 eight arm-like processes, from which groups of short, knobbed 

 tentacles arise (fig. 197). 



The genital organs extend on the oral wall of the umbrella into 

 the arms as eight band-shaped, plicated ridges. They run along in 

 pairs at the lower part of each septum in the gastric cavity. The 

 ovum, according to Fol, undergoes a complete segmentation, which 

 results in a single-layered blastosphere. This becomes an oval, two- 

 layered larva, which becomes ciliated, swims freely about, and finally 

 attaches itself. The further development probably takes place 

 directly without alternation of generations. 



17 



