THE SHIP-WORM. 



439 



So strange are many of the structures, and so unexpected are many of the habits of 

 these creatures, that zoologists are often in great doubt as to their true position in the 

 natural kingdom. For, while many anatomical details are closely analogous to those of 

 the molluscs, others are equally analogous to those of the higher zoophytes, and it is 

 not always easy to hold the balances with an even hand. 



In these curious beings we find the first indications of propagation by buds spring- 

 ing from the body of the parent just as a bud springs from the branch of a tree, and 

 the perplexing alternation system is sometimes found in the Tunicata. Both these 

 systems will be explained when we come to describe the zoophytes. 



PELON/EA. Peloaxa corrugata. 

 SEA-SQUIRT.- -Asc/d/um hyallnum. BOLTENI A. -Bo/ten/a reaiformls. 



SYNTETHYS. Syatetbys Hebrldtcus. 

 CYNTHIA. Cynthia tnorus. 

 BOTRYLLUS.-Bo*/y//us polycyclus. 

 CLAVELLINA.-C7aveJ/toa lepldlformls. 



Without enumerating the various details of anatomical structure in these creatures, 

 we may mention that the animal is composed of two sacs, one inside the other, and 

 that the functions of nutrition and respiration are performed, as in the bivalves, by 

 means of two orifices, one of which admits and the other expels the water, which laves 

 the respiratory apparatus and brings food to the organs of nutrition. 



In our present arrangement, which is that followed by Mr. Woodward, the Tunicata 

 are divided into three families, easily distinguishable by the eye. The members of 

 the first group are called Solitary Ascidians, those of the second Social, and those of 

 the third, Compound Ascidians, their characters being sufficiently explained by their 

 names. The name Ascidian is of Greek origin, and is the diminutive of a word sig- 

 nifying a water skin, such as is used in the East. 



