mouth, and the posterior leading into the anus. The alimentary 

 canal is much bent on itself. The opening of the pharynx is sur- 

 rounded by a fringe of tentacles, arising from the peritoneum or 

 lining membrane next to the outer test. The capacious pharynx 

 is perforated with slits, and serves as a respiratory cavity compar- 

 able with that of the worm, Balanoglossus. At the bottom of this 

 respiratory sac opens the true mouth, which communicates by an 

 (Esophagus with the stomach, while the intestine is twisted so that 

 the anus opens near but posterior to the mouth. There is a ner- 

 vous ganglion on the dorsal side of the body situated at a point 

 between the two external orifices, sending threads to the two 

 openings in the test and the pharynx. The heart is a short tube 

 open at both ends. Its action may be beautifully seen in the 

 transparent Perophora of our coast. The current of blood is 

 momentarily reversed, so that each end becomes, as Huxley re- 

 marks, " alternately arterial and venous." 



Such in general terms is the structure of a typical simple 

 ascidian as well as the compound ascidians, and the Pyrosoma 

 and Sal pa. The aberrant Appendicularia is, as has been observed, 

 provided with a tail, and resembles the tailed young of the higher 



The ascidians are, for the most part, hermaphrodites, the ovary 

 and testis being lodged in the same individual. 



Development While Milne-Edwards discovered that the larvae 

 of certain ascidians were tad-pole like, Kowalevsky, in 1866, 

 studied the development of the ascidians and threw a flood of 

 light on their history. The following account is an abstract of 

 his classic memoir. The early stages of most ascidians is typified 

 by the mode of growth of Phattusia mamittata Cuv., while the 

 mode of growth from the free swimming larval period to the adult 



confirmed by Kupffer and others, while exceptional modes of de- 

 velopment were pointed out by Lacaze-Duthiers and also Kupffer, 

 who found that the larva} of Molgula have no tail. 



While some ascidians, such as Perophora, increase by budding, 



method^of reproduction is°by eggs and sperm cells. The eggs of 



yolk-kin, but surrounded by a layer of jelly containing yellow 



