12 



and in it the embryo lay inrlosed in its foetal coverings. These foetal membranes will be more fully treated of elsewhere, 

 suffice it to say here, that the little foetus was closely enveloped in the amnion. (PL VI, figs. 2 and 3). 



On a closer examination of the external form of this embryo, it unfortunately proved to be very much deformed 

 and injured, especially in the anterior, more pointed end (PL I lig. 1). The external form of the head could not therefore be 

 determined, nor was any indication of either fore or hind extremities observable. On the other hand the convex surface of the 

 back was distinct separated from the injured front portion by a sharp furrow, thereby giving prominence to the more rounded 

 back part of the. trunk. At the posterior end was observed a blind fossa underneath, ventrad of the tail. The tail was 

 plainly to be seen lying in folds, and bent upwards against the ventral surface. In front of it. the remains of the umbilical 

 cord might be observed (fig. 1, u.). 



On looking at the ventral surface of the embryo, it proved to be injured to such an extent, that no clear idea 

 ot its external form could be gathered. On the other iianJ. with regard to the posterior end of the body, there could be 

 traced a long, relatively well-developed, cylindro-conical tail, lying in a sigmoid curve, and in front of it the remains of the 

 detached navel forming an irregular oval surface (PI. I, fig. 2 c and u). 



In viewing the embryo's right side (fig. 3). there are no exact particulars to be gained of the shape of the head, 

 visceral cleft, etc., so that only vague conjectures can be made. Remains of the umbilical cord and the enlargement behind 

 it (u) may be seen. The hinder part of the body here too. appears smooth and uninjured. The hollow at the posterior end 

 together with the cylindrical tail are noticeable. 



In a dorsal aspect, the furrow separating the injured from the uninjured parts is to be clearly seen; the body 

 tapers towards the end, where the tail is bent forward against the ventral surface. The body does not appear to be 

 symmetrical, a fact which must doubtless be attributed to a deforming sigmoid curvature in the long axis, and which is 

 confirmed by the longitudinal sections made. 



How far this may be a normally-developed embryo seems doubtful after external examination. The injury to the 

 fore part of the embryo, especially the head, may perhaps be attributed to a too great shrinking caused by the preserving 

 tinid, and consequent great deformity and partial breaking away of the epidermis. This, however, is only partly confirmed 

 by a microscopical examination, which rather points to an interrupted developement, with already commenced degeneration. 

 The possibility of cadaveric changes may, on the other hand, be almost excluded, as the specimen was preserved fresh. I 

 have had good opportunity of ascertaining that the deformity of, and injury to the front part of the body were not due to 

 its preparation being commenced after hardening, as the opening of the amniotic bag was made from behind and on the 

 back, so that in any case, the injuries, if any, could only have been slight and superficial, caused by the instruments 

 during this process. 



Drawings of the embryo were made by Dr. F. Nansen (PL I, figs. 1 — -1). As the examination of the external form in 

 this specimen could lead to no further explanation or information, it was coloured in borax carmine and imbedded in paraffine. 

 and microtomised in longitudinal sections (162 sections). 



On examining the sections with a low magnifying power (Zeiss, obj. aa oc. 2, drawn with an Abbes camera) it 

 appeared, as before, that the fore part of the embryo was exceedingly deformed, and had also, as regards the histological 

 structure, undergone a degenerative change. The immediate impression received is that a deforming, retrogressive change 

 has taken place, in which the histological elements have been injured. 



It is, however, noticeable, that this histological change principally affects and is most marked in the anterior part 

 of the embryo, corresponding with the facts apparent on external examination. 



When the sections are examined with a low magnifying power, the segmentation of tlie convex, dorsal parts of 

 the body becomes more and more distinct, the nearer the sections approximate the median line. The proto vertebræ, or 

 mesoblastic somites (PL I, figs. 5 and 6, Seg) reveal themselves partly as a closer, more undifterentiated mass of cells 

 which, in many sections, especially in the dorsal region, are separated by the embryonal connective tissue with elongated 

 cells and a clear, homogeneous ground substance, partly by the appearance of an incipient cartilage formation, in the shape 

 of short, true cartilage vertebræ. Fragments of the chorda dorsalis are seen in many of the sections (fig. 6, ch). I was 

 able to count more than 40 segments. The segmentation of the tail part was not complete. Tafel I, fig. 5 shows the 

 segmentation of the lateral region outside the medullary tube, while in fig. 6 may here and there be seen longitudinal sections 

 of the cliorda, the clear lines arranged in rows representing the incipient cartilage vertebræ. 



The outline of the medullary tube (fig. 6, med> is distinctly seen, but while the elements constituting it have, in 

 the fore part, the appearance of a shapeless mass in which no distinct cell elements are to be discovered, there may he found in 

 many places in the hinder part that corresponds with the embryonal body's uninjured portion, distinct epithelial cells, arranged 

 to some extent in rows, but always rather curved, with many artificial lacuna\ In the fore part of the embryonal body, 

 enlai'gements of the medullary tube may be plainly seen, which are most naturally inter})reted as the embryonal brain vesicles 

 (fig. 6, cb). In a few sections situated laterally as regards that represented in fig. 6, there is a smaller brain vesicle 



