304 MR. Gt. BROOK ON SOME POINTS IN 



heart. It is tlus lower return branch to the heart which would 

 seem to be the homologue of the large vessel in Oyclopterus, which 

 distributes the blood around the yolk before it is again collected in 

 the heart. In Motella, also, this vessel passes over what is left of 

 the yolk on its way to the heart. ^Further work, however, is needed 

 on this point before any true analogy can be established. 



During the first few days of the embryo's free existence, the 

 pectoral fins far outstrip the ventrals in dimensions. A refer- 

 ence to fig. 11 shows the pectorals as large, flat, leaf-like expan- 

 sions, while the ventrals are thick and short, with an undulating 

 margin, and are deeply pigmented. 



Agassiz (" On the young stages of some Osseous Fishes," part 

 iii., Proc. Amer. Acad, of Arts and Sciences, new series, vol. ix. 

 1882) expresses a doubt whether the young stages which he 

 has figured as Motella argentea belong to that genus, and are not 

 rather the young of Onus, in which the ventrals are developed 

 to an extraordinary degree in the young, reminding one of the 

 specialized development in Flying-Fishes. I am not aware 

 whether Agassiz's figures have since been identified j but if they 

 really represent Motella, it is easy to see how the ventral fin, as 

 represented in my fig. 11, could be developed so as to agree 

 with Agassiz's pi. vii. fig. 1. 



There appears to be one point in which the Gradidse differ in 

 their development from all other Teleosteans of which the deve- 

 lopment is known, and that is the late period at which the anus 

 opens externally on the ventral surface. The exact time at which 

 this takes place is not known. Hyder figures the young of the 

 Cod 7 days after hatching (" Contrib. to the Embryog. of Osseous 

 Fishes : " Eeport of the Commissioner of Fish and Fisheries 

 for 1882. "Washington, 1884, pi. xii.), with the intestine and 

 anal gut having no opening externally ; and in the oldest embryos 

 I have had of Motella (i. e. 6| -7 days after hatching) I have 

 found the same to be the case. It would appear, then, as if the 

 yoUng Gradidse were not in a position to take solid food at nearly 

 so early a period in their development as is usually the case with 

 Teleostean embryos. 



There is another point which is worthy of notice in the deve- 

 lopment of pelagic ova, namely the length of time which the 

 embryo spends within the egg. The following is a list of 

 the principal species of pelagic eggs observed, where the observers 

 state the time of hatching : — 



