166 CTENOPHOR^. Part II. 



principles. DeBlainville and Lesson ai-e the only zoologists who have associated 

 heterogeneous types with the CtenophoriB. 



In now closing this sketch of the anatomical characters of the Ctenophora^, I 

 have only to add a few remarks upon some controverted points of their structure, 

 wath a view of eliciting further investigations, and preventing some mistakes from 

 being more widely circulated. I have already stated that there exists no distinct 

 muscular system in the Ctenophora\ The appearance of fibres resembling muscles 

 arises from the peculiar form of the large cells (PI. IP. Fhj. 24) forming the 

 spherosome, aliout which more may be found in a subsequent chapter, where 

 I shall also consider the true nature of the parts which, from their position and 

 appearance, have been mistaken for nerves. 



The CtenophoraB move in two different ways; and the two kinds of motion 

 are pi-oduced by different parts. The more energetic movements, which propel 

 the body forward, are produced by the contraction of the various systems of 

 motory cells hereafter to be described, and take place by jerks when they are 

 most 2:)0werful, though during a slow, onward pi-ogress they produce a more sliding 

 motion ; besides, these animals are kept hovering in the Avater )jy the unceasing 

 and rapid motion of their locomotive flappers. Of course, during a slow progress, 

 the movements of these rows of flappers combine with the action of the motory cell 

 systems, while in a more rapid progression they can contribute l;)ut little, if any thing, 

 toward a change of place. As the mode of locomotion of the Discophoraj differs 

 in different lamilies according to their different form and the part their various 

 appendages take in their movements, we must postpone a more detailed account 

 of these differences to another chapter. Suffice it here to say, that the long 

 tentacles of Pleurobrachia and the broad lobes of Bolina become important auxili- 

 aries in regulating the motions of these types. That the powerful contractions 

 of the spherosome greatly modify the form of the Ctenophora3 is now generally 

 understood ; but I would warn the student against a belief that the form of these 

 animals is on that account less characteristic than in other animals. A bird flying 

 has certainly a very diflerent appearance from what it 2)resents when at rest; but, 

 whatever position it may assume, its form is always characteristically its own. So 

 is it with the Acalephs in general, and, more especiall_y, with those Ctenophora? 

 which are capable of performing the most diversified movements. As soon as the 

 mode of execution of these movements is fully understood, the form preserves all 

 its characteristics. 



The chymiferous system of all Ctenophora; requires more careful study than 

 has generally Ijeeu devoted to it. The mode of ramification of its main trunks, the 

 form of the funnel, the course of its Ijranches and their anastomoses, are very 

 characteristic of the different fiiniilies. That these details should have been neg- 



