392 Dr. 0. A. L. Morch on the Systematic Value of the 



male intromittent organ is first found among the Reptiles, and 

 becomes more and more developed among the higher Vertebrata. 



That this fact is not in consequence of aquatic habits is evi- 

 deut by comparing the Cetacea and Sea-serpents, which are 

 provided with a true male organ. 



A similar fact may be observed among the Articulata, of 

 which the Insects only may have a true male organ. 



Among the Mollusca the Androgyna are provided with the 

 most developed male organ, and which seems to be the most 

 sensitive. The male organ of the Exophallia is always external, 

 not retractile, sometimes concealed in a furrow of the right ten- 

 tacle (e. g. Viviparus). The Pseudophallia have no male organ*. 

 The copulation is probably effected in the same way as among 

 Batrachians ; but direct observations are wanting. The male 

 Acephala disperse their sperm, which is taken up by the females 

 like the pollen by flowers. The few observations on the copula- 

 tion of Acephala are very problematical. My synopsis confirms 

 the rule of Prof. Agassiz that laud-animals are more perfect than 

 marine ; but this rule may be explained in the sense that the 

 divisions with the largest number of terrestrial forms always are 

 the superior. Thus, among the Vertebrata, the Thennaliaf are 

 higher than the Psychisemia, containing the greatest number of 

 aquatic forms. The lowest class, Acephala, is entirely aquatic 

 and chiefly marine. Among the Pseudophallia, Helicince are the 

 only terrestrial, and Neritinee fluviatile. The number of ter- 

 restrial genera is considerably increased among the Exophallia ; 

 thus Cyclostomacea are truly terrestrial, Ampullar iae, Paludirue, 

 Melanice, and Potamidce fluviatile. Among Androgyna are the 

 greatest number of terrestrial genera. 



There is the same concordance with the law of Prof. Owen, 

 " that the multiplicity of organs indicates inferiority in organiza- 

 tion." As was shown in a former paper, the duplicity of the 

 organs of Acephala descends as the system ascends. 



The development of the young is of less systematic value than 

 is generally believed : this is proved in the Crustaceans, the 

 marine species having a larval form very different from the 

 fluviatile species (Astacus fluviatilis and A. mar inns). All larvae 

 of marine Mollusca swim by means of a velum, which in the 

 marine Acephala, Chiton and Dentalium is changed to a flagel- 

 lum. In the melicertigene Gasteropoda (Rhachiglossata) the 

 larva loses the velum before it leaves the egg-case. The larva 



* In the ' Voyage de l'Uranie' is represented a Neritina with something 

 like a short male organ between the month and right tentacle, but which 

 seems not to have been observed in the European species. 



t The difference between hot- and cool-blooded animals seems not to 

 be sufficiently insisted upon in the modern systems. 



