Notes on the Development of Sepia. 105 



XIV. — Notes on Prof. E. A. Minchin's Preparations of the Early 

 Stages in the Development of Sepia. By J. H. Koeppern 



(Glasgow University). [Plates I. to X.] 



(Read 20th December 1909. Received 14th February 1910.) 



Through the kindness of Prof. J. Graham Kerr, I was enabled to study 

 the slides which Prof. E. A. Minchin prepared at Naples in 1892, of the 

 early stages in the development of Sepia. Prof. Minchin's drawings of the 

 preparations are so admirable that it would be regrettable to refrain from 

 publishing them, and expedient to add such notes on the preparations as 

 might be of use in elucidating the problem of Cephalopod development. I have 

 to record my thanks to Prof. Kerr for suggesting this work and for his help 

 and advice. My thanks are also due to Dr W. E. Agar for his kind interest. 



The ova of Argonauta and Loligo are known to form three polar bodies 

 (Ussov) ; in Sepia, however, only two polar bodies have been observed. 

 Although Vialleton describes the first polar body as being frequently 

 binucleated, he mentions that he never saw a third polar body. It was, 

 consequently, not surprising that three distinct polar bodies were evident 

 in some of the preparations under observation (e.g. Fig. 1). 



There seems to be no determinate relation between their situation and the 

 direction of the first cleavage furrow, nevertheless, the latter always occurs in 

 very close proximity to the polar bodies. As no preparations of the germ calotte 

 at a stage before the formation of the first cleavage spindle were available, it 

 was not possible to corroborate Vialleton's statements regarding a causal con- 

 nection between the course of the uniting pronuclei and the first cleavage plane. 



The process of cleavage and the nuclear figures correspond with Vialleton's 

 drawings. 



After the germ calotte has been divided up into a considerable number of 

 blastomeres, the elongated ones radiating at the periphery, the " blastocones," 

 gradually assume club shape. The handles of the clubs become thinner, 

 until they form delicate rays fading away into the membrane of protoplasm 

 surrounding the yolk. Simultaneously, the basal parts of the " blastocones " 

 divide into polygonal cells. These become detached from the germ calotte 

 and are much modified in their outline. The protoplasm surrounding the 

 nuclei wanes, until a stage is reached where the nuclei may be observed 

 to be situated on the "files radiales" surrounded by a halo of protoplasm. 

 At first the nuclei are arranged concentrically round the germ calotte and 

 karyokinetic figures are in evidence, 1 the axes of the spindles being directed 



1 Owing to the dense arrangement of the chromosomes and the lack of suitable sections 

 the number of the chromosomes could not be satisfactorily ascertained. Twelve rod- 

 shaped chromosomes were observed in several telophases. 



VOL. XVIII. H 



