454 NOTES AND MEMORANDA. 



Studied, given various results as to the possession of motility. 

 In the Crustacea, excepting the Cirrhipedia, it appears to be well 

 established that the spennatozoids are incapable of automatic 

 movements. In the Arachnida on the other hand this is not so 

 well established, whilst in the Insecta alone does it appear that 

 movements of the spermatozoids have been habitually observed. 

 So far then the motile character of the spermatozoids of Limulus 

 tends to separate it from the Crutascea, though our knowledge 

 of the spermatozoa of the Arachnida does not enable me to add that 

 there is any special approximation in this matter between Limulus 

 and the members of that group. A comparison of the morpho- 

 logy and development of Limulus and of Scorpio renders it abso- 

 lutely necessary in my opinion to class Limulus and its fossil allies 

 under the Arachnida as a sub-class, " Branchio})ulmoiiata." 



E. Kay La>kester. 



The Early Developmental Changes in the Reptilian Ovum. 



— Professors Kup])fer and Benecke have recently published a very 

 interesting note on this subject. Their observations were made 

 on Laceria agilis and on Enujs Enropea, in both of which types 

 they found the embryonic changes to be closely alike. Segmen- 

 tation takes place exactly as in birds, and the resulting blasto- 

 derm, which is thickened at its edge, spreads rapidly over the 

 yolk. A small embryonic shield makes its appearance in the 

 centre of the blastoderm shortly before the yolk is half enclosed. 

 It is somewhat jiyriform, and mainly distinguished from the re- 

 mainder of the blastoderm by the more columnar character of its 

 constituent epiblast cells. At the narrower end of the shield, 

 which may be spoken of as posterior in relation to the future 

 embryo, an invagination takes place, and gives rise to a sack, 

 the blind end of which is directed forwards. The opening of the 

 sack may be spoken of as the blastopore. A linear thickening 

 of the epiblast arises in front of the blastopore, along which the 

 medullary groove soon a])pears. In the cephalic region the 

 medullary groove flattens out, and posteriorly the two medullary 

 folds diverge, and enclose between them the blastopore, behind 

 which they again meet. On the completion of the medullary 

 canal the blastopore becomes obliterated ; but there can be but 

 little doubt, although the authors of the paper do not appear to 

 touch on this point, that on the closure of the medullary folds 

 the medullary canal remains in direct communicatian with the 

 cavity of the invaginated sack, so that the latter has exactly the 

 same relation to the medullary canal as the embryonic structure, 

 wliich I have called "the jjostanal section of the alimentary canal " 

 in Elasniobianchii. 



At the time when the above- described invagination appears. 



