24 THE PELAGIC STAGES OF YOUNG FISHES. 



Species allied to Motella. 



Nos. 1, 2, 15. 



Plates XII. and XIII. 



Among the pelagic fish eggs occurring at Newport, one of the smallest 

 and rarest is that figured in Plate XII. The average size of the egg is about 

 .70 mm., ranging from .68 to .75 mm. The globule is comparatively large, 

 measuring usually about .17 mm., but varying now and then from .165 to 

 .175 mm. 



The period of occurrence of these eggs is closely limited, so far as we 

 have been able to observe, to the month of July, the earliest record being 

 June 27, and the latest August 4. Within this period the egg was found 

 only on nine occasions ; and, with two exceptions, only two or three at a 

 time. Thirty -six were obtained on July 19, and thirty on July 29. Among 

 those of July 19, nine had from two to four globules each, the rest having 

 only one. In every case where more than one globule was found, complete 

 coalescence took place' within twenty-four hours. As Fig. 1 of Plate XII. 

 represents the youngest stage obtained, we are unable to say whether the 

 occurrence of two or more globules is the rule in the earlier stages. 



Although we have not been able to obtain a complete series of the stages 

 of development, we have enough to warrant the opinion that this species is 

 allied to Motella. The eggs which have been referred to Motella by Mr. 

 Agassiz are a little larger (.75 to .84 mm.), with a single large globule (.15 

 to .16 mm.); while those of M. rmisteUa are of about the same size, varying 

 according to Brook* from .655 to .731 mm. (longest diameter). The size of 

 the globule in M. mustella is stated by Brook to be only .11 mm., and this is 

 remarkably small as compared with the eggs we have studied. 



Our observations on the occasional occurrence of several globules and 

 their ultimate coalescence to form a single globule, taken in connection with 

 those of Brook, make it probable that both in the species under consideration 

 and in Motella the fresh-laid egg has, normally, more than one globule. 

 The presence of more than one globule is regarded by Brook as an abnor- 

 mal development, which leads to irregularities often fatal to the development 

 of the embryo ; but this view is certainly not sustained by a comparative 

 study of the occurrence of oil-globules in other species. 



* Brook, George. Liunean Society's Journal. XVIII., 18S5, p. 298. 



