832 PROFESSOR W. C. M'INTOSH AND MR E. E. PRINCE ON 



brownish belt along the inferior margin. The black spots on the posterior part of the 

 first and second dorsals are very distinct, and the dark belt of the anal is densest at the 

 posterior end. In life the whitish streaks often have a bluish appearance. 



The remarkable length of the ventrals in the post-larval ling resembles the condition 

 described by Alex. Agassiz, in Onus* and in Motella. 



Motella mustela, L.t — The ova of this species abound in the sea from March to May, 

 and those in the tanks shed their ova freely in April. The unimpregnated egg on its 

 escape has a diameter! of 73 mm., the measurements given by Mr Brook (No. 31) ranging 

 from "655 to 731 mm. The hyaline capsule is slightly corrugated, and the entire yolk- 

 surface presents a series of minute oleaginous particles. Mr Brook's larvae emerged 

 on the fifth or sixth day, but at the laboratory the development was less rapid at the 

 beginning of May, probably from the much colder surroundings. Thus ova, in which 

 the blastoderm had enveloped two-thirds of the yolk (probably more than three days 

 after impregnation) on the 4th May did not emerge till the 11th May. Nine proto- 

 vertebrae were visible on the 5th, and the blastopore closed on the 6th May. The 

 optic vesicles were well defined, but the otocysts did not appear till 5 p.m. of this day, 

 the first sign of their cavity being a very fine slit. Brook gives the length of the 

 newly hatched larvae at 2*25 mm. About the sixth or seventh day after hatching the 

 mouth resembles that in the young plaice, the lower jaw projecting very much 

 (PL XVII. fig. 2). An oil-globule occurs in the small portion of the yolk still remaining. 

 The marginal fin is finely fibrous, and in the caudal region fine threads stand out 

 in the moribund animal. The notochord shows very large cells, those in the tail 

 being rounded and forming a single linear series, while the anterior are smaller, more 

 numerous, and irregular. An interesting condition of the termination of the neurochord 

 is seen at this time, for it exhibits a distinct lobular dilatation (ne) having a fine central 

 canal (mc) which can be traced a long way forward. This terminal nervous enlargement 

 (ne) projects beyond the end of the notochord (ne) (PL XV. fig. 4). The skin has a very 

 irregular surface many from granular papillae. Three days later (May 11th) most of the 

 embryos had died, as they are somewhat delicate forms ; but the survivors (see fig. 2, 

 PL XVII.) show a beautiful iridescent area behind the pectoral fins, probably from the 

 swim-bladder. The yolk-mass has been absorbed and the median dorsal fin has diminished. 

 The mandible (mn) is still prominent. 



Proceeding to consider what may be called the post-larval stages, procured in St 

 Andrews Bay, we note that Alex. Agassiz,§ in one of his papers on the young stages 

 of " Osseous Fishes," in which he made known the remarkable development of the ventrals 

 in a form doubtfully regarded by him as a Motella, speaks of it as Motella argentea, 

 Rhein., though he added that it might be a species of Onus described by Collet. 



* Op. tit., p. 273. 



t The egg and larval form figured by Mr Cunningham (op. cit., p, 105, pi. vii. figs. 3, 4) evidently belong to 

 Motella. 



X In parts of an inch their diameter is "0283, and the oil-globule - 0033 or less. 

 § Proc. Araer. Acad. Sti. and Arts, vol. xvii., July 1882. 



