192 



Introduction to Animal Morphology. 



(Sipunculus, Kcfcrstein}. In Bonellia the eggs are- 

 developed in a longitudinal, medio-ventral fold. 



The embryos are free-swimming, ciliated, with a 

 ciliary girdle and an anterior mouth dorsally over- 

 lapped by a bilobate upper lip ; ventrally, there is 

 either a single lower lip or several ciliated processes 

 (five in Phascolosoma minutum) the homologues of 

 the trochal discs of Rotifera. These in Sipunculus 



A, larva of Phascolosoma ; r, upper lip ; , lower lip ; z', intestine ; m, mouth ; 

 B and C, mollusc larva.-. 



develop into the tentacles. Similar lobes are not 

 confined to Gephyrean larvae, but reach their greatest 

 development in the form Actinotrocha (probably the 

 larva of the Chaetopod Phoronis). The metamor- 

 phoses in development resemble those of the Echino- 

 dermal larvae, as only part of the larva is concerned 

 in the development of the adult. 



They are divisible into two orders : 



i. Inermia bristles and vascular system, none. Family 

 i. Sipunculidae cylindrical, with the mouth at the tip of the 

 retractile proboscis surrounded with tentacles, often with 



