44 PROFESSOR OWEN ON INDIAN CETACEA. 



Imperfect as may be the cetacean record, it yields several series of differential cha- 

 racters, — as, e.g., in the proportion of the rostral to the cranial part of the skull, from 

 Physeter simus to Physeter macrocephalus and Platanista — in the degree of expansion of 

 tlie back part of the maxillaries, exemplified, step by step, in Balmia, Delphinus, PJio- 

 ccena, Zi-pJdus, Euphysetes, and Physeter, again culminating in Platanista — in the number 

 of teeth, from zero [Balcena and old Delpkinapteri), through Monodon, ZipJmcs, Euphy- 

 setes, to the multitude of teeth in Delphinus, Cuv. 



The formation of germs of teeth in parts of the jaws of fcetal or young individuals of 

 species which are edentulous in the full-grown individuals, the examples of which 

 are too well known to need citation here, are, perhaps, amongst the most significant of 

 the gradational modifications, above referred to, being due to deviations in offspring 

 from the characters of parents. 



Such departures or variations may have been slight in the first instance, few and far 

 between in the members of a contemporary generation, and rare exceptions to the rule of 

 hereditary likeness ; but, occurring in the course of many generations, through long lapse 

 of time, they might lead to " long-snouted" and " short-snouted" breeds, and to others 

 exemplifying the various observed cranial and dental modifications of cetacean structures. 



In such conjectural mutations of specific characters may be discerned a fore-ordained 

 law of deviation from primitive type, through the operance of which the ocean 

 has at length become peopled with so many strange modifications of the cetacean 

 structure. 



But such instances of exceptional freedom from the trammels of family likeness seem 

 to be independent of external influences. The ocean has none of those diversities of 

 condition which the dry land shows, and is exempt from the few which in fresh waters 

 may be invoked to account for varieties in the species of fish. It is true that the trout 

 [Salmofario) of the mountain-streamlets is small, while that of the wide river or wider 

 lake is large ; but no such differences can be invoked to explain the origin of the 

 dwarf Euphysetes or the giant Physeter : both ha\e alike the unlimited seas for their 

 range. 



But the same river may have the pike, the carp, the salmon, the eel, &c. ; these 

 modifications of the piscine type exist in waters of the same temperature, same rate of 

 flow, and same nature of bed. Where can we here discern selective influences equiva- 

 lent to produce such changes of structure ? The hypothesis is still less conceivable in 

 regard to the ocean. The various Cetacea of the Indian seas exist in a medium of the 

 same nature, exempt from any influence of the earth beneath them, or of aught that 

 may there live and grow. The external influence or power that could " select " the 

 maxillary wall of the circumnarial basin, e. g., in Hyperoodon, Ziphius, Euphysetes, 

 Physeter, Platanista, is inconceivable. 



But the occasional departure from parental type, manifested by a so-called abnormal 

 or monstrous proportion of the nasal or facial plate of the maxillary, may accord 



