PKOGRESS OF MICROSCOPICAL SCIENCE. 103 



resemblances existing between the adult Polyzoon and tbe adult 

 Ascidian, so far as they may be supposed to indicate any close affinity 

 or community of origin, arc thus doubly denied by the diiferences of 

 form and structure, both in the adults and in the larvso. The Ascidians 

 are also likely to be removed by these new discoveries, not only entirely 

 away from the Polyzoa, but to an equal or greater distance from all the 

 rest of the Mollusca ; and even if we could in the face of embryology 

 still maintain our comparison between the two structiu-es, we should be 

 contrasting the Polyzoa, not with a typical mollusk, but with an animal 

 whose own position is very uncertain. He can think of no fundamental 

 molluscan characteristics, either in the Brachiopods or Polyzoa, which 

 ally them with the Lamellibranchs (clams), except those which join 

 them still more closely to the Ascidians. Therefore, it seems clear, 

 that if we separate the Ascidians from the Lamellibranchs, w^hich they 

 so closely resemble in their general adult characteristics, on account 

 of their different developments, we must also, in turn, remove the 

 Polyzoa from the Ascidians, and should logically regard the similarities 

 of the two as analogies arising in different structures, and not as affinities 

 derived from some conmaon ancestor. Thus cut off from its quondam 

 molluscan allies, our Polyzoon has but one refuge ; its development 

 points concisely to a vermian ancestor, and to this source we must 

 relegate both it and its nearest ally, the Brachiopod. 



Professor Agassiz's Future Dredging Operations, — Professor Agassiz 

 has accepted an invitation extended to him by the American Coast 

 Survey Bureau to take passage on the iron coast-survey steamer, which 

 has just been built at Wilmington, Delaware, and which sails for the 

 Pacific coast in September next. The expedition will take deep-sea 

 soundings all the way, and extensive collections of specimens will be 

 made for the Museum of Comparative Zoology at Cambridge. Secretary 

 Boutwell has written to the Secretaries of State and Navy, asking that 

 naval and other officers may be instructed to afford such courtesy and 

 assistance to the exploring party as may be desirable. We learn also 

 that Count Pourtales, of the Coast Survey, and Dr. Hill will accompany 

 the expedition. 



Structure of Stephanurus dentatus, or Sclerostoma pinguicola. — 

 Dr. W. Fletcher gives a somewhat lengthy accoimt of this worm. It 

 appears not to have been correctly known in America till last year. A 

 specimen was brought to Dr. Fletcher in 1866 by a farmer whose 

 hogs were dying of cholera. He had removed the lungs of several, and 

 also cut out fragments of the liver, all of which were spotted over with 

 little cysts containing the worms ; in the bronchial tubes down to the 

 minutest branches, they were found in abundance and in situations 

 where no one could have placed them. With these specimens his 

 conclusion was that they were the Filaria bronchialis of Owen, or 

 Strongijlus bronchialis of Cobbold ; and not having at this time made 

 microscopic examination of this well-known kidney worm, the relation- 

 ship between them did not occur to him at that time. In November, 

 1870, while demonstrating the portal circulation in the liver of a pig, 

 full grown, he observed a worm which measured an inch and a half in 



