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Appendices to Fifth Annual Report 



mantle, rests on an ill-defined basement layer of longitudinal cells, 

 associated here and there with large aggregations of nuclei (PL XIII. fig. 

 2, no). The areolar cells of the stroma are nucleated. 



The mature-sperm follicles of a full-grown adult seen in section are 

 circular, irregularly rounded, or sinuous in outline. They are densely 

 filled with spermatozoa. The sperm mother-cells are crowded, spherical, 

 refractive bodies, containing the spermatozoa in all stages of development. 

 The liberated spermatozoa arrange themselves in streaks or bands which 

 radiate from a point in some follicles, while in others they are pinnate (PI. 

 XIV. fig. 1, sf). The bands may unite in the central area of the follicle 

 and form reticulations. As the spermatozoa are carried off by the efferent 

 action of the cilia in the canals communicating with the follicles, 

 translucent, protoplasmic filaments are left (PI. XIV. fig. 1, pf). The 

 spermatozoa are evidently grouped on those filaments. A mass of free 

 spermatozoa was found in the genital tube which is figured in section 

 (PI. XIII. fig. 4, s). In young forms, half an inch in length, the mantle 

 can accommodate only a single series of sperm-follicles, they being 

 proportionately so large as to occupy the whole breadth of the mantle 

 (PI. XIV. fig. 2, */.) 



The mature egg, after extrusion, is quite spherical and very opaque, on 

 account of the large development of deutoplasmic (vitelline) granules 

 (PI. XII. fig. 1). The vitellus appears greenish-brown by transmitted 

 light. The egg membrane is distinct. The nucleus and nucleolus are not 

 visible in a normal, mature egg, a less opaque region marking their position. 

 The hyaline investment referred to above as noticeable around the intra- 

 follicular eggs, forms a broad, very translucent sheath to the ripe extruded 

 egg. It may be slightly stained and crumpled by eosin. It is presumably 

 adherent to mature eggs naturally extruded, certainly so in the case of 

 artificially liberated ones. "Whatever other function it may perform, it is 

 of service as a protective covering to the egg, and as a medium by which 

 spermatozoa are detained. Many spermatozoa wriggle into it, and cause 

 the egg to rotate. It may be seen, in some cases, to enclose segmenting 

 ova (PI. XII. fig. 9, hy), spermatozoa being still present in it. No micropyle 

 has been observed in it. 



The vitelline membrane is clearly defined. If ruptured by osmotic 

 action, the nucleus escapes as a spherical body bounded by a definite 

 membrane, and enclosing the nucleolus (PI. XII. fig. 6, n). 



Fertilisation is effected in the laboratory by mixing spermatozoa with 

 ova, both being liberated by mincing the tissue containing them in sea-water. 

 The head of a spermatozoon is rounded posteriorly, and tapers forward to 

 a point (PI. XII. fig. 33), the point being longer than that represented by 

 Lacaze-Duthiers.* Eipe spermatozoa are free and independent, and when 

 liberated artificially, are accompanied by a whitish secretion. They dis- 

 seminate very rapidly when put into sea-water. Their vitality is note- 

 worthy, and has been referred to by Professor M'Intosh.t 



When the ova are extruded they descend to the bottom of the beaker, 

 hence, after allowing time for the attachment of the spermatozoa, it is 

 possible to remove completely the milky secretion which accompanies both, 

 and which, if not carefully removed, would speedily cause putrefaction, and 

 would lead to the early death of the embryos. The time taken by the 

 spermatozoa to effect fertilisation varies considerably, according to the 

 depth of the hyaline zone, the vigour of the spermatozoa, and other more 

 occult conditions. The first token of success is the protrusion of the polar 



* In the Report for 1886 the spermatozoa are inadvertently described as having 

 thelhead rouoded anteriorly, whereas it is pointed, and does not taper to the tail. 

 flLoc. cit., p. 150. 



