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manhattensis. Accounts of the embryology of the latter have 

 been published. Tellkampf (1871), working with this species, 

 observed that the eggs were liberated from the cloacal chamber, 

 and he described their transformation into mammariae, each 

 mammaria subsequently giving rise to a single tadpole larva. 

 Kingsley (1882), working as he supposed with the same species, 

 denies the existence of mammariae and states that the embryos 

 develop in an " ovarian pouch" until the tadpole stage. Van 

 Name (1912, p. 466) has helped to clear the situation by identify- 

 ing a number of Tellkampf's specimens as M. manhattensis. 

 Tellkampf is correct in his first observation that the adult 

 liberates eggs from the cloacal chamber, but development from 

 this point has apparently been confused with other forms. Sev- 

 eral points of difference are found between Kingsley's account and 

 recent observations of M. manhattensis, but these discrepancies 

 have been satisfactorily cleared by the suggestion of Grave (1926) 

 that the species with which Kingsley worked is M. citrina. In 

 addition, Grave gives measurements for the egg and larva and 

 pictures the free-swimming tadpole form of M. manhattensis. 



At least one statolith is always present in the tadpole of M. 

 manhattensis, and this large, black, spherical body persists long 

 after the animal becomes attached. This organ was found still 

 evident in numerous embryos developing in Syracuse watch 

 glasses until 15 days old. In those animals in which the statolith 

 persisted, the siphons were still widely apart, while in animals in 

 which the statolith had disappeared the siphons had moved into 

 the same relative position as that characteristic of the adult. 



Thus it is shown that M. manhattensis has a free-swimming 

 larval period and a statolith, while M . robusta has neither. 



Beside the specific differences found in their development, 

 other minor differences distinguish the adult forms of the two 

 species. 



M. manhattensis, as pointed out by Van Name (1912), is found 

 most plentifully in shallow water, always attached, and usually to 

 eelgrass, piling, or rocks near the surface. M. robusta, on the 

 other hand, is found on sandy or muddy bottoms, unattached, 

 and in deeper water, that is, at depths varying from 60 to 80 

 feet. 



Moreover, M. manhattensis is symmetrical, while M. robusta is 

 asymmetrical. The asymmetry in the latter is probably brought 

 about during its development and is caused by the movement 

 of the siphons to one side. In this position the siphons are 



