84 DIVERGENCE AND PARALLELISM 



in relation to the origin of vertebrates (1875), 

 it would not have led to what many zoologists 

 are constrained to regard as a series of false 

 homologies ; and per contra it would not have 

 led to many interesting discoveries. 



There are two factors which conspire to 

 beguile a morphologist into spurious relations 

 and vain imaginings : these are the potency of 

 convergence and the weight of coincidence. A 

 very eminent French zoologist, who enjoyed the 

 respect and veneration of all who came directly 

 or indirectly within the sphere of his influence, 

 the late Professor Henri de Lacaze-Duthiers, 

 thought from the beginning to the end that 

 the Ascidians (Tunicata) are related to the 

 Mollusca. In apparent confirmation of this belief 

 he discovered the case of a simple Ascidian, a 

 species of Molgula, which develops without the 

 intervention of the usual tailed larva ; and then 

 he discovered a form in the Mediterranean which 

 he called Chevreulius, but which had already 

 been named Rhodosoma from the Pacific, where 

 the atrial and buccal siphons lie within a hinged 

 valve which can be opened and closed like the 

 valves of a lamellibranchiate mollusc. 



It is indeed extraordinary to relate, in Dr 

 Gaskell's words, that the infundibulum "lies just 

 anteriorly to the exits of the third cranial or 

 oculomotor nerves ; in other words, it marks the 

 termination of the series of spinal and cranial 



