114 REPORT— 1860. 



where it was discovered by Mr. Byerley, and where the present writer had found it 

 in the same rock-pool, with its congener A. cristata. He submitted the following 



Catalogue of the Nudibranchiata of the Mersey and Dee. 



1. Doris tuberculata. Mersey and Dee ; common. 



2. Johnstoni. Mersey and Dee ; once or twice. 



3. proxima. Mersey and Dee ; common (nowhere else). 



4. bilamellata. Mersey and Dee ; abundant. 



6. pilosa. Mersey and Dee ; not uncommon. 



6. subquadrata. Dee ; once (the second known specimen). 



7. depressa. Dee ; once. 



8. Polycera Lessonii. Mersey ; occasional. 



9. ocellata. Mersey and Dee ; occasional. 



10. Ancula cristata. Mersey and Dee ; common. 



11. Tritonia Hombergii. Mersey and Dee ; occasional. 



12. plebeia. Mersey and Dee ; occasional. 



13. Dendronotus arborescens. Mersey and Dee ; common. 



14. Doto coronata. Mersey and Dee ; very common. 



15. Eolis papillosa. Mersey and Dee ; common. 



16. coronata. Mersey and Dee ; common. 



17. Drunmiondi. Mersey and Dee ; very common. 



18. rufibranchialis. Mersey and Dee ; not uncommon. 



19. Landsburgii. Mersey and Dee : rare. 



20. concinna. Mersey ; common (the second known locality). 



21. ■ olivacea. Dee (once taken). 



22. aurantiaca. Mersey and Dee ; common. 



23. picta. Mersey and Dee ; not uncommon. 



24. exigua. Mersey ; apparently rare. 



25. despecta. Mersey; common. 



26. Embletonia pallida. Mersey (the only known locality) ; very rare. 



27. Antiopa cristata. Dee ; occasional. 



28. hyalina. Dee (the only known locality) ; very rare. 



On Recurrent Animal Form, and its Significance in Systematic Zoology. By 

 Cuthbert Collingwood, ALB., F.L.S., §c, Professor of Animal Phy- 

 siology in Queen's College, Liverpool. 



The object of this paper was to call attention to the frequent recurrence of similar 

 forms in widely-separated groups of the animal kingdom ; similarities, therefore, 

 which were unaccompanied by homologies of internal structure. These analogies 

 of form had greatly influenced the progress of classification, by attracting the atten- 

 tion of systematizers, while as yet structural homologies were imperfectly under- 

 stood ; and, as a consequence, many groups of animals had been temporarily located 

 in a false position, such as bats and whales by the ancients, and the Polyzoa and 

 Eoraminifera in more modern times. These resemblances in form were illustrated 

 generally by the classes of Vert ebrata, and more especially by the various orders of 

 Mammalia, — the Invertebrata affording, however, many remarkable examples. 

 Since no principle of gradation of form would sufficiently account for these ana- 

 logies, the author had endeavoured to discover some other explanation, and had 

 come to the conclusion, that the fact of deviations from typical/orm being accom- 

 panied by modifications of typical habits, afforded the desired clue. Examples of 

 this were given, and the principle educed, that agreement of habit and economy in 

 widely separated groups is accompanied by similarity of form. This position was 

 argued through simple cases to the more complex, and the conclusion arrived at 

 that, where habits were known, the explanation sufficed ; and it was only in the 

 case of animals of low organization and obscure or unknown habits, that any serious 

 difficulty arose in its application ; so that our appreciation of the rationale of their 

 similarity of form was in direct ratio to our knowledge of their habits and modes 

 of life. ba_conclusion, by a comparison of the Polyzoa with the Polyps, it was 



