78 ASCIDIANS CHAP. 
(genus Anurella, Lacaze-Duthiers), the embryo does not become 
converted into a tailed larva, the development being direct 
without metamorphosis (see Fig. 42, C). The embryo when 
hatched gradually assumes the adult structure, and never shows 
the features characteristic of larval Ascidians, such as the 
urochord and the median sense-organs. Fig. 42 shows an 
Ascidiid (A), a Cynthiid (B), and this exceptional Molgulid (C), 
type of larva, and three forms of Compound Ascidian larvae, the 
Distomatid (D), the Botryllid (E), and the Diplosomatid (F). 
Fic. 42.-—Larvae of various Ascidians. A, Ascidia mentula, Linn.; B, Polycarpa 
glomerata, Alder; C, Anurella roscovita, Lac.-Duth.; D, Distaplia magnilarva, 
Della Valle; E, Polycyclus renieri, Lamk.; F, Diplosomoides lacazii, Giard. 
(Mostly after Lahille. ) 
In the Molgulidae the viscera are characteristic in position 
and appearance. The alimentary canal lies on the left side of 
the branchial sac, and the intestine forms a long narrow loop 
directed in the main transversely. The pericardium and _ heart 
are on the middle of the right side, and behind them is placed 
the single sac-like ductless renal organ, generally occupied by 
one or more concretions. The gonads are in most cases on both 
sides of the body, in front of the intestine on the left, and in 
front of the heart on the right; but in Hugyra there is no gonad 
on the right side, and in some other forms the gonad on the left 
side is absent. (For Oligotrema, see p. 111, note.) 
There are a number of British Molgulidae, the two commonest 
