2 Prof. Miillcr on the Anatomy and Development 



once Columbus and Covtez, The discoverer — he has gleaned all 

 its riches. For it so happens that Sars^ the only investigator 

 Avho preceded him in the study of the development of the Echi- 

 noderms, had not the good fortune to meet with instances of the 

 ordinai-y course of development^ but only with a case, excep- 

 tional among the Echinoderms, but differing less from the em- 

 bryogenic phsenomena of other animals. 



Nor are we indebted to the Professor for a widening of our 

 embryological knowledge alone. A more exact knowledge of 

 development involved the necessity for, and at the same time 

 furnished the key to, a more accurate idea of the adult structure 

 of the Echinoderms. 



The ordinary Echinoderms sufficiently try the patience of the 

 anatomist; and any one who has ever endeavoured to dissect a Ho- 

 lothuria, must recollect the feeling of despair with which he re- 

 garded the knotted, glairy, eviscerated mass, which was too often 

 the reward of all his care and caution. Undaunted by the great 

 practical difficulties, however. Prof. Miiller has entered into these 

 complementary investigations (which are contained in the fourth 

 and fifth treatises of the foregoing list) ; the errors, difficulties, 

 and contradictions which formerly infested the subject have been 

 cleared up and rectified, and the structure of the Ophiuridfe, 

 Asteridse, Echinidse, and Holothuriadfc is now capable of being 

 reduced to broad general propositions. Without by any means 

 claiming for the celebrated Berlin physiologist the merit of dis- 

 covering facts of organization, due to Tiedemann, to Valentin, to 

 Krohn and others, it yet cannot be denied, that under his hands 

 these facts have first assumed their due importance, and become 

 moulded into a consistent whole. Under his authority, then, 

 without always caring to indicate the original sources of infor- 

 mation, we shall give the following summary of some ])oints of 

 the organization of the Ophiuridse, Asteridse, Echinidse and Ho- 

 lothuriadje, as preliminai-y, and indeed necessary, to a proper 

 comprehension of their genetic phenomena. 



It is not, however, necessary for our present purpose to enter 

 upon the anatomy of any other systems of organs than the water- 

 vascular system, the blood-vascular system, and the nervous 

 system. 



In all the families cited, the fundamental part of these three 

 systems consists of three distinct rings, surrounding the oeso- 

 phagus ; the blood-vascular ring lies innermost, the water-vas- 

 cular ring next, the nervous ring outermost. 



The hlood-vascular I'ing, besides the branches which it gives 

 off, is always connected with two vessels which run along oppo- 

 site sides of the intestine [Halothuria] ; and in Asterida and 

 Echinidse there is a distinct tubular heart which connects the vas- 



