030 ANNELIDA I ACTINOTROCHA LARVA OF SIPUNCULUS. 



puzzle to Zoologists ; since, although there could be no doubt of its 

 being a Larval form, there was no clue to the nature of the adult 



produced from it, until this 

 Fig. 328. was discovered by Krohn to be 



a Sipunculide Worm.* The 

 process of transformation has 

 been subsequently more fully 

 described by Dr. A. Schneider, 

 and seems to consist in a sort 

 of turning-inside-out of the 

 Actinotrocha. A long convo- 

 luted tube which was pre- 

 viously to be seen within the 

 cavity of its body, closed at 

 one end and opening at the 

 other upon the ventral sur- 

 face, is the body- wall of the 

 future Worm ; this evert3 

 itself, and issues from the 

 body of the Larva, at the 

 same time completely taking - 

 in its Intestine, which is 

 doubled together (as in a her- 

 nial protrusion), so that the 

 Mouth and Anus are brought 

 into close apposition with each 

 other at the anterior end of 

 the body. The entire body- 

 wall of the Larva, with the 

 hood and the anal circlet of 

 cilia, disappears ; the tentacles 

 remain for a time at the an- 

 terior extremity of the tube, con- 

 tracted into a close circlet ; this 

 circlet is subsequently cast-off, 

 however, by a kind of moult, 

 at which period the whole surface of the body has become 

 clothed with cilia. The development of the Circulating apparatus 

 commences before the transformation, and this apparatus comes 

 soon afterwards into active operation, f 



491. An even more extraordinary departure from the ordinary 



* 'Ueber Pilidium und Actinotrocha,' in "Mtiller's Archiv.," 1858, 

 p. 293 ; see also Wagener, ' Ueber den Bau der Actinotrocha branchiata, 

 op. cit., 1857, p. 202. 



f • On the Development of Actinotrocha branchiata ' in the "Monatsbe- 

 richte" of the Berlin Academy for Oct. 1861, p. 934, and in "Ann. of Nat. 

 Hist.," Ser. 3, Vol. ix. (1862), p. 486.— The Author has met with Actino- 

 trocha, sometimes in large numbers together, in Lamlash Bay, Arran; 

 and Dr. Cobbold has taken it in the Frith of Forth. 



Actinotrocha branchiata : — a, Epis- 

 tome or hood ; b, Anus ; c, Stomach ; 

 d, Ciliated Tentacula ; e, Mouth. 



