DEVELOPMENT AND LIFE-HISTORIES OF TELEOSTEAN FISHES. 793 



centre a nuclear portion (n) can be made out, and this usually remains clear and un- 

 changed, while around it very minute particles of black pigment (pt) develop. These 

 particles increase so rapidly that the bases of the pseudopodia become much darkened, 

 and a centrifugal transference commences, the minute particles flowing along the ramify- 

 ing arms, until a pale steel-tinted stelliform body becomes distinctly outlined. The tint 

 grows in intensity, and finally shows the dense black colour characteristic of the completely 

 developed corpuscle. In many cases by their extension these black corpuscles intermingle 

 so as to interlace their arms in a complex manner, and even coalesce, as was noticed by 

 Lereboullet, who also observed the persistence of the central pale nucleus in each 

 corpuscle (No. 93, p. 579). 



The variations in the disposition of the pigment in different forms is noteworthy, and 

 its diagnostic utility has been already mentioned. The time at which pigment appears is 

 also remarkable. Lereboullet found in Perca that it develops earlier and more abund- 

 antly than in Esox, though in both forms it overspreads the yolk-sac (No. 93, 

 pp. 579-586, 610). It is very precociously developed in the flounder, and comparatively 

 late in the whiting. 



During the later larval stages the epidermis becomes very irregular — rounded pro- 

 tuberances appearing especially over the cranial and facial regions (PL IX. fig. 3 ; PL 

 XVII. fig. 4). Many of these are sensory enlargements, and described elsewhere, but 

 enlarged mucous cells develop, especially in the region of the snout. These open 

 superficially, and doubtless are protective in function — bathing the young embryo exter- 

 nally with a gelatinous secretion. The contents of these large mucous cells stain very 

 deeply, and are especially noticeable in sections of the plaice, though in Cyclopterus and 

 others they also form a noteworthy feature. 



No cilia are apparently developed upon the embryonic integument, nor do fine 

 immovable hairs occur as in Petromyzon and its young stage — Ammoccetes. The serial 

 sensory papillae (PI. VI. figs. 8, 8a) send out fine filiform processes (pip), but they are 

 local, and probably pushed through from the neurodermis below. The development of 

 scales as protrusions from the corium which burst through the epiblastic integument, as 

 well as the formation of iridescent plates in the stratum Malpighii, belong to a late post- 

 larval stage. In some young forms, it is true, a brilliant iridescent appearance is seen in 

 the abdominal region ; but this is occasionally due to the enlarged swim-bladder, the fishes 

 in certain cases remaining translucent, and almost colourless in the post-larval stages, when 

 all the more important structural features of the adult are assumed. In such forms, again, 

 as the post-larval Anarrhichas, the whole abdomen is iridescent. 



Ova and Generative Organs. — As soon as the segmental ducts have reached their 

 final position on each side of the dorsal aorta, a strand of peritoneal (splanchnopleuric) 

 cells passes below them. They thus become grouped on the inner side close to the 

 mesentery (PL VII. fig. 1). These cells become aggregated, and produce an irregular 

 contour especially in the posterior region — where the alimentary canal is more distant 

 from the notochord, and the median mesenteric membrane is better developed. They 



VOL. XXXV. PART TIL (NO. 19). 6 I 



