238 



BY THE DEEP SEA. 



are provided with a more or less intricate machinery for 

 carrying out all the functions of life. But so it is ; and here 

 is the typical plan of arrangements inside our Ascidian. Here 

 the necks of the bottle are marked a and n respectively, and 

 a, by which the current of water flows in, is called the oral 

 orifice. Just inside is a series of tentacles (), and below 

 these we are in the branchial chamber 

 (c), where the great work of supplying 

 the blood with oxygen is carried on. 

 The walls consist of a lattice -work of 

 blood-vessels, through whose tissues the 

 blood takes up the molecules of the life- 

 supporting gas. Below this chamber 

 the gullet opens and is continued into 

 the stomach (g), and beyond it is the 

 intestine (h), which in turn opens out 

 through the anus (/) into another roomy 

 chamber, the atrium (m) or atrial 

 chamber, with its external opening (n). 

 O is a ganglion or small brain, and f 

 indicates the heart. 



Now in order to get a correct idea of the Tunicates as the 

 group in which the Ascidians are included is called I wish 

 you to note the figures d and e in the same diagram. 

 You will see that they indicate two separate envelopes. The 

 outer of these, represented by the thick dark line, is of a 

 tough, leathery nature, and is much akin to vegetable cellulose 

 in its character a fact that caused some little commotion in 

 scientific circles years ago, when it was first satisfactorily 

 made out, for prior to that date cellulose was considered to be 

 purely a vegetable product. This outer coat is known as the 

 tunic, or test, and from the fact that all the species are enclosed 

 in such a tunic, the group gets its name Tunicata. The inner 

 coat represented in the diagram by the clear space between 

 the thick and thin marginal lines, is of a more delicate, more 



DIAGRAMMATIC SECTION OF . 

 AN ASCIDIAN. 



