432 NOTES AND COMMENTS [juste 



Development of Lepidosiren. 



A valuable contribution to our knowledge of the Dipnoi will be found 

 in Mr. Graham Kerr's paper on the external features in the develop- 

 ment of Lepidosiren garadoza, Fitz., communicated to the Eoyal Society, 

 May 4. The abstract with which we have been favoured summarises 

 the more important points as follows : — 



The egg is very large, 6*5 to 7 mm. in diameter. It is surrounded 

 by a special capsule, at first thick and almost jelly-like in appearance, 

 later on (after fertilisation) thin and horny. Outside this was found 

 in rare cases a thick jelly resembling that of the frog's egg. The egg- 

 is without a trace of dark pigment. Segmentation is complete, re- 

 sembling most nearly that of the egg of Amia, and leads to a condition 

 with an upper hemisphere of small cells with large segmentation 

 cavity, and a lower of large yolk cells. Gastrulation begins with 

 the appearance of a row of depressions, or a continuous groove along 

 about one-third of the whole extent of the margin between small and 

 large cells. During its progress the small-celled portion spreads over 

 the lower yolk cells by the addition to its margin of small cells split 

 off from the yolk cells. As the groove referred to deepens into a slit 

 to form the archenteron, it becomes gradually shorter, and the event- 

 ually complete blastopore is a crescentic slit only about a quarter of 

 the length of the original groove. The medullary folds soon appear 

 running forwards from the blastopore. There is no trace externally of 

 a blastoporic or protostomal seam running along the back between the 

 medullary folds. The folds are low and inconspicuous, and they are 

 continued into one another behind the blastopore, which becomes the 

 anus. There are only slight traces of overarching of the medullary 

 folds to enclose a neural canal. During the later stages of intraoval 

 development, the posterior end of the body becomes much more con- 

 spicuously folded off the yolk than the head end. The Lepidosiren 

 hatches out as a tadpole-shaped larva, still completely devoid of dark 

 pigment. Just about the time of hatching the cloacal opening closes 

 temporarily. As the larva develops it becomes extraordinarily amphi- 

 bian-like. It possesses large pinnate external or somatic gills, four 

 on each side, corresponding to branchial arches I., II., III., and IV. 

 A large cement organ is also present, which during its early stages is 

 of the characteristic crescent shape so usual in the embryos of Anura. 

 Pigment begins to appear about ten days after hatching — first in the 

 retina, then over the dorsal surface, especially anteriorly. The larval 

 condition lasts during the first six weeks after hatching. Towards the 

 end of this period the cement organ undergoes atrophy. The somatic 

 gills atrophy later. During the process of their doing so, the Lepido- 

 siren passes through a condition in which the stumps persist, evidently 

 corresponding to that well known in the young Protoptcrus, the group 

 of external gills with their common stalk having come to be situated 



