[26] Artificial impregnation may be effected without difficulty by squeezing out into the same vessel the ova and spermatozoa of a ripe female and male. The fertilized eggs are easily reared. Petromyzon Planeri breeds during the second half of April.
[27] In Calberla’s figure, shewing the development of the notochord, the limits of mesoblast and hypoblast are wrongly indicated.
[28] Scott informs me that he has been unable to find the hyomandibular pouch in larvæ larger than 4.8 mm. My material of the stages when it should be present is somewhat scanty, but I have as yet, very likely owing to the imperfection of my material, been unable to find Scott’s hyomandibular pouch either in my sections or surface-views. Huxley describes this pouch as present in the form of a cleft in later stages; I have failed to find his cleft also. The vessel interpreted below as the branchial artery of the mandibular arch was only imperfectly investigated by me, and I was not sure of my interpretations about it. Scott however informs me by letter that it is undoubtedly present.
[29] Schneider (No. [85]) states that in the full-grown Ammocœtes the opening is situated between the third and fourth pouches. This is certainly not true for the young larva.
[30] Max Schultze’s statements as to the structure and histology of the brain are very inadequate in the present state of our knowledge.
[31] Langerhans loc. cit. describes the eye of the Ammocœtes in some respects very differently from the above. Very probably his description applies to an older Ammocœtes. The most important points of difference appear to be (1) that the vitreous humour is all but obliterated; (2) that the iris is much better developed.
[32] Cyclopædia of Anat. and Phys. Article ‘Ovum.’