THE GONOSOME. 



49 



There is some difficulty in (Ictcrmiiiiiig the exact morphology of the acrocyst. In its usual 

 form it seems to consist of a sim- 

 ple extension of the endothcca Fig- 20. 

 of the gonophorc, protruded as 

 a hernia-like sac through tiie 

 summit of the gonangium, when 

 the whole becomes surrounded 

 by a thick gelatinous-looking 

 envelope, which is excreted from 

 the outer surface of the sac, and 

 which shows no appearance of 

 true structure, though distinct 

 zones of deposition may occa- 

 sionally be observed in it. 



In CalyceUa lacerata the 

 spadix itself, as was first shown 

 by Dr. S. Wright, is, with the 

 surrounding endotheca and ova, 

 carried upwards u[)on the blasto- 

 style, by whose elongation these 

 various parts ai'e protruded from 

 the summit of the gonangium, 

 and the endotheca thus becomes 

 a true acrocyst and excretes from 

 its outer side the usual thick 

 gelatinous investment (woodcut, 

 fig. 22). The peculiarity of the 

 acrocyst in this case is found 

 in the presence within it of the 

 spadix, which, however, is de- 

 pressed by the enlarging ova, 

 and forced back into the bottom 

 of the sac. 



In the interior of the acro- 

 cyst the ova pass through certain 

 stages of their development, and 

 ultimately escape as free ciliated 

 embryos by the rupture of its 

 walls. 



From the observations of Strethill Wright it would appear that in IJ'rijIilia {AlrudyJis) arenosa, 

 a gymnoblastic species, the ova escape, by the rupture of the sporosac, into a gelatinous mass which 

 is a secretion from the outer surface of the summit of the sporosac, to which it remains adherent, 

 and that in this gelatinous nidus they become converted into planulaj, and then escape into the 

 surrounding water. It is plain, however, that the simple gelatinous secretion which thus affords 



7 



Gonangium, with Its contents, from Laomedea repens, Alliu., showing the 

 compound blastostyle. 



A, General viewj B, plan of transverse section, a, gonangium ; b, lower portion 

 of blastostyle continuing simple; c, opercular summit of blastostyle; d, separate 

 tubular branches into which the blastostyle has become divided ; «, the endotheca; 

 /, ramifications of spadix; (^, an ectodermal membrane, connecting the divisions of 

 the blastostyle with one another. 



