109 



forms of Mammalia, which he had progressively worked out in pre- 

 vious palaeontological writings. 



As examples of Anatomical Monographs, 1 may refer to the me- 

 moir on the Lepidosiren annectens, in the Linnsean Transactions for 

 1839 ; * On the Anatomy of the Rhinoceros,' in the Zoological 

 Transactions, and to the Papers * On the Eustachian Canals in the 

 Crocodile,' ' On the Carapace and Plastrum of the Chelonia,' * On 

 the Dentition of the Phacochcerus or Wart-Hog,' and ' On the Ex- 

 ogenous Processes of Vertebrse ' in the Philosophical Transactions. 



The value of microscopical research in comparative anatomy has 

 been already alluded to, and a fresh instance of its importance is 

 given in the elaborate researches on the subject of the Teeth, the first 

 results of which were communicated in a report to the British Asso- 

 ciation at the Meeting at Newcastle in 1838, and they were ulti- 

 mately embodied in the great work entitled ' Odontography,' com- 

 prising one volume of text and an atlas of 168 plates, in which the 

 diversified modifications of the dental tissues in all classes possessing 

 teeth are fully illustrated. 



The minute structure of scales and other dermal appendages of 

 Fishes has been studied microscopically by Professor Owen, who was 

 led by the phenomena he observed to oppose the views of the develop- 

 ment of scales by excretion, which M. Agassiz had contended for; and 

 he demonstrates the close analogy which exists between the dermal 

 bony tubercles and spines of the cartilaginous fishes and their teeth. 



Professor Ov/en's views have been confirmed, the analogy extended, 

 and a variety of beautiful modifications of tooth-like structure de- 

 monstrated by Dr. Williamson in his papers recently published in 

 onr Transactions. 



Of the application of the microscope by Professor Owen to the 

 solution of some of the mysterious problems of generation, examples 

 will be found in his ' Lectures on the Comparative Anatomy and Phy- 

 siology of the Invertebrate Animals,' published in 1843; in those 



* On the Generation and Development of Animals,' published in 

 1849-50; and in his work ' On Parthenogenesis, or the successive 

 production of Procreating Individuals from a single Ovum,' also pub- 

 lished in 1849. In the latter work Professor Owen shows the intent 

 of the ' cleavage process,' as it has been called, to be that by which 

 the spermatic principle is distributed throughout the germ-mass : 

 and he there points out the consequent relation of such inherited 

 subdivision of the spermatic principle to future developments of em- 

 bryos in virgin parents. As propounded in this work, the theory be- 

 came capable of application to many other cases besides that to which 

 it was first applied. 



The progress of Natural History has added many analogous in- 

 stances of virgin-generation to that of the Aphides. In all these 

 Professor Owen calls attention to the proposition of the primary 

 cell -structure of the impregnated germ, which is retained in the pro- 

 creative larvse.. Dr. Steenstrup has very ably and very ingeniously 

 generahzed the phenomena in question in his well-known essay on 



• Alternation of Generations.' 



