152 



EMBRYOLOGY 



transverse ones, and correspondingly the subsagittal ribs exhibit a larger 

 number of swimming jjlates. In the further course of development the 

 meridional vessels pass into the oral lobes, and their lower ends become 

 bent ; in this way the subtransverse vessels come to be the longer. 

 Whereas in the adult the lower ends of the vessels in each lobe are 

 united in such a way that the two subtransverse vessels communicate 

 with each other, and the two subsagittal vessels with each other, at this 

 stage the subtransverse vessel forms with the subsagittal vessel of the 

 same quadrant a closed system of tubes (Fig. 73). 



Fig. T3. — Medusiform staple of Eiicharis mufficoniis (after Chun). A, view of 

 the sagittal plane. B, view from above : on the right-hand side the ribs are 

 omitted : m, stomach ; I, oral lobes ; (, rudimentary tentacular apparatus ; st, sub- 

 transverse, .«s, subsagittal, meridional vessel. At x the subsequent connection of 

 the vessels is indicated by dotted lines. 



There now follows a stage of medusiform habit, the course of the 

 vessels remaining about the same (Fig. 73), in which, as in the adult, 

 the sagittal diameter already exceeds the transverse. In this larva, 

 which, like a Medusa, moves through the water by the pulsating action 

 of its oral lobes, a complete degeneration of the tentacular apparatus 

 (() occurs ; this is replaced in the succeeding Boliua stage by a new 

 tentacular fundament. In this stage is reached the form of body and 

 distribution of vessels typical of the Lobatse, for, on the one hand, 

 the connection of the subtransverse with the subsagittal vessels is 



