ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 165 



The fact that Loph/uft piscatorius has a prolonged pelagic period is 

 now made clear. Insufficient data led to the view that the pelagic 

 period was very short. The specific gravity of the eggs and the loose 

 binding together in a gelatinous matrix of extended surface ensure for 

 the large eggs a prolonged period of flotation, first at the surface, and 

 afterwards in the upper layers. Later on the power of flotation is 

 increased by the extraordinary length and spread of the membranous 

 pelvic fins of the larvre ; and there are other interesting adaptations. 



The remarkable sheets of spawn are discussed at some length. The 

 spawning period in the northern parts of the North Sea extends from 

 February or March to July. It begins at least as early as January in 

 the Mediterranean. A careful study of the records points to the con- 

 clusion that the main spawning area in the North is beyond the limits 

 of the North Sea, and that the Atlantic itself may be the main spawning 

 area. The sheets of spawn probably drift for great distances. J. A. T. 



Secondary Sex Characters of Elasmobranchs. — W. Haeold 

 LeiCtH-Shakpe {Journ. Morphologt/, 1920, 34, 247-65, 12 figs.). In 

 the male Elasmobranchs the basal element of the pelvic fin is prolonged 

 to form a stout backwardly directed skeletal rod supporting a portion of 

 the fin specially modified to form a copulatory organ, called the clasper. 

 It is rolled up in a manner resembling a scroll, so as to form what is 

 practically a tube along which the spermatozoa pass, injected in sharks 

 and dogfish by a very muscular apparatus, the siphon. In the skates 

 the place of the siphon is taken by the clasper gland contained in a sac 

 which it completely fills. Other accessory structures may be present on 

 the claspers, such as the spurs and the like in Acanthias and the fan- 

 like terminal expansion (the rhipidion), most developed in skates, whose 

 function is to spray the spermatozoa in all directions in a radiating 

 manner. The author describes the clasping apparatus in Scyllmm 

 catulus, S. canicula, Acanthias vulgaris, and Raia circularis. In 

 8. catulus there is a pair of accessory sacs (parasiphons), smaller than 

 the siphons, and nearer the median line, dorsal to the skeletal rod. 

 They are accessory to the siphons. In 8. canicula the parasiphons are 

 vestigial. The clasper groove or tube is filled with spermatozoa by a 

 gradual flow through the apopyle (anterior proximal opening). Copula- 

 tion ensues, and the claspers are bent forward so that the apopyle is 

 closed. Muscular contraction of the siphon-wall follows, and the 

 spermatozoa are ejected by the flush of sea-water into the oviduct of 

 the female. The posterior end of the ovyiuct is naturally dilated to 

 admit of the inclusion of the claspers. In young females it is closed by 

 a hymen. The roughened rhipidion, with backward pointing denticles, 

 passes anterior to this dilation and serves for close and secure attach- 

 ment. In S. canicula the rhipidion is vestigial. The siphon of the 

 living animal contains sea-water. The siphons arise in development 

 apparently as invaginations of ectoderm. The siphon wall consists of 

 an internal membrane of stratified epithelium, a broad layer of circular 

 muscles, a ventral band of longitudinal muscle, and, dorso-lateral in 

 position, a longitudinal muscle-band external to the whole. In Acanthias 

 vulgaris the apopyle is considerably removed from the cloaca, the 

 actually closed portion of the clasper tube is short, the rhipidion is 



