197 



Figure 147: Ophiura sarsi. Cleavage. 



A — two blastomeres; B — four blastomeres; C — eight blastomeres. 



View from the vegetal pole and laterally. 



at the 32-blastomere stage. On the other hand, in Ophiocoma echinata (Grave, 

 1898) and Gorgonocephalus caryi (Patent, 1970a) blastomeres of small size 

 have been reported. The blastula does not emerge from the envelope with the 

 appearance of cilia, sometimes it remains immobile inside it for two hours. 

 Then the cilia begin to beat, initially slowly, but soon more and more rapidly. 

 The blastula turns around on its axis, the speed of rotation increases, the 

 envelope is ruptured, and the blastula begins to swim (Figure 148). Some- 

 times hatching does not occur. Patent (1970a) noted that in Gorgonocephalus 

 caryi the blastula does not leave the envelope and that it is devoid of cilia. 

 Cilia also do not develop in Amphioplus abditus (Hendler, 1977). In Ophiura 



M 2 



Figure 148: Ophiothrix fragilis (McBride, 1907). 



Blastula. 



M 1 — primary mesenchyme; M 2 — secondary mesenchyme. 



