400 DR W. CARMICHAEL M'lNTOSH ON THE STRUCTURE OF THE 



offer great facilities for such investigations, and I have had no difficulty in rearing 

 the Borlasise at a long distance from the sea. 



The ova on deposition in the flask-shaped capsules are uniformly granular 

 and opaque ; and when broken up, are seen to be composed of a granular oily 

 matter, which forms streaks and rounded masses, and is not cellular, as described 

 by E. Desor. The clear, semi-transparent spot mentioned by the latter as 

 occurring in the ova after deposition is seldom visible, though the germinal 

 vesicle (a) and dot (b) are apparent enough in the centre of a pale oleaginous 

 space, while they are yet in the body of the female (Plate XIII. fig. 8). The 

 cleavage of the vitellus generally commences on the second day, when in some 

 it is found divided into two and in others into four parts. As first pointed out 

 by Max Schultze, Desor committed an error when he stated that the irregularity 

 of the divisions of the vitellus distinguished this species from other animals. 

 The divisions proceed regularly and somewhat rapidly; for ova which presented 

 four lobes at 9 a.m. were found at 1 p.m. broken up into a number of rounded 

 masses, so that the ovum had a nodulated or mulberry-aspect. No clear spot 

 was observed in the centre of these secondary masses. During the next four or 

 five days the changes which ensue in the ova consist chiefly of sub-divisions of 

 the vitellus, which daily become finer. There is now a pale spot in the ovum, 

 and a few free granules and cells in the flask, as noticed by Desor. The ova 

 gradually become smoother in the outline from sub-division of the vitellus, and 

 then only a few nodules appear here and there on the otherwise even cir- 

 cumferences. E. Desor found the ova ciliated on the twelfth and fourteenth 

 days, Max Schultze on the eleventh and twelfth, and I have struck the average 

 amongst the British examples on the latter date. The ova, again, which had 

 been left entirely above the water-line did not develop so quickly. At first the 

 ciliation does not cause the mass to revolve, but subsequently this motion takes 

 place with vigour. They continue in this condition for about a month, and then 

 a further change ensues in the contents of the flasks (Plate XIII. fig. 4); and the 

 latter drawing will explain E. Desor's discovery, as well as enable us to correct a 

 slight inaccuracy into which he has fallen. The opaque ciliated mass previously 

 noticed bv-and-by shows a double outline under pressure, caused by the develop- 

 ment of the young Borlasian within the ciliated coating; indeed, at an advanced 

 stage, as in the middle of the flask represented in Plate XIII. fig. 4, the embryo 

 seems as if shrouded in a layer of fatty cells and oil-globules (b), within which it 

 distinctly moves. In such a condition the animal readily escapes from its invest- 

 ment, and at the upper part of the same flask a free example («) is seen. E. Desor 

 commits an error in his excellent description, when he states that the cells in the 

 interior of the embryo are the "residue of the vitellus destined for the support 

 of the animal ;" they are nothing else than the cells in the developing wall of 

 the alimentary canal. The large dark ciliated mass (c) at the lower part of the 



