382 



TUNICATA. 



sents the rudiment of the branchial sac (pharynx). The rest of the 

 alimentary canal (d) develops as an outgrowth at the posterior dorsal 



Fig. 177. — Embryo of Molgula macrosiphonica (after Kupffer). d, rudiment of the 

 alimentary canal ; es, endostyle ; ,/', body-processes ; i, rudiment of the inhalent 

 orifice; n, nervous system : r, spherules of reserve nutriment. 



angle of the primary enteric vesicle. The inhalent and exhalent 

 orifices, the endostyle, the gill-slits, etc., develop as in other Ascidians. 



3. Doliolum. 



The development of the egg in Doliolum seems to form a direct 

 sequence to that in other Ascidians. As in the latter, a larval form 

 occurs which propels itself by means of a swimming tail. r l his larva 

 was first described by Krohn (No. 85), and later by Gegenbaur 

 (No. 78), Kefersteix and Ehlers (No. 81), Grobben (No. 79), and 

 Uljanin (No. 86). To the latter author we owe, fm-ther, almost 

 the only statements we have as to the embryonic development of 

 DoUohtui, which is very insufficiently known. 



The mature egg of Doliolum, surrounded by follicle-cells, reaches 

 the atrial cavity of the mother from which it is soon ejected into the 

 surrounding water. Occasionally, however, part of the embryonic 

 development seems to take place within the atrial cavity. As a rule, 

 the egg is fertilised only after its expulsion, and then surrounds 

 itself with a homogeneous membrane. This membrane (Fig. 178, m) 

 which soon rises up from the surface of the egg in such a way 

 that a space filled with fluid can be seen between it and the egg, 



