SENSES OF THE TUNICATA. 



327 



guished poets of Germany. The Salpae progress by the alternate 

 contractions and dilatations of their tubular body. In this 

 manner the chains, as if obeying a common impulse, glide 

 along with a serpentine movement, and are often regarded by 

 sailors as sea-snakes. 



Before quitting the Tunicata, a few points of interest in their 

 simple history remain to be noticed. Despite their humble 

 organisation, they have a heart which, as may easily be ascer- 

 tained in the transparent species, is subject to strange alter- 

 nations of action. For after having received for a minute or 

 two the blood from the branchiae, and propelled it to the 

 system at large, it will at once cease to pulsate for a moment 

 or two, and then propel the 

 blood to the branchial sac, 

 receiving it at the same 

 time from the system gene- 

 rally. After this reversed 

 course has continued for 

 some time, another pause 

 occurs, and the first course 

 is resumed. It is very pro- 

 bable that many of the 

 Tunicata are able to hear 

 and to see. In Chelyosoma, 

 organs have been discovered 

 whose structure seems to 

 indicate that they are des- 

 tined for the transmission 

 ■of sound, and the Ascidise 

 have frequently around the 

 •extremity of their tubes a 

 row of coloured points simi- 

 lar to the imperfect organs 

 of sight present in the ma- 

 jority of the bivalve Acepha- 

 lans. Thus a closer exami- 

 nation of the lower animals is constantly bringing new faculties 

 to light, and the further we penetrate into the secrets of their 

 life the more we find occasion to admire the power and wisdom 

 •of their Maker I 



z 2 



Inner or tinder side of the Bupenor plated 

 surface of Chelyosoma Macleayanum. 



a. Branchial orifice, o. Anal orifice. 



c. Muscles bordering the carapace-plates. 



d. Central hexagonal plate, e. Surrounding plates. 

 /. The nerve-ganglion and nerve-fibres. 



g, A. Auditory apparatus, 

 t. Bow of tentacles, anterior to the cesopnagus. 

 J. Stomach. A- Fart of the intestine. 



