PERIPATUS. 705 



In the four largest embryos which he extracted from the uterus, Dr Hansen 

 observed a most remarkable feature. From the articular membrane which connects the 

 head with the protergum, there issued an unpaired nuchal organ, slender at the base 

 but rapidly increasing in volume, which became lacerated during the removal of the 

 embryo. " This organ," he considered, " must be in connection with the interior wall of 

 female genital organs and thus serve the nutrition of the young ones." 



While taking out the two smallest of the embryos, which he was able to procuri' 

 without destroj'ing the specimen, the head was broken off in each case, which seemed 

 to him to indicate " that also these specimens had been fixed by an organ from the 

 neck." Remarking upon the probably nutritive function of this nuchal organ, Dr Hansen 

 does not hesitate to give it as his opinion that the very anomalous mode of propagation 

 of Hemimerus is of great systematical importance', and marks it as the t}-pe of a distinct 

 fiimily allied to the Forficulina. 



To my mind the nuchal organ of Hemimerus is homologous with the corresponding 

 trophic vesicle of Paraperipatus novae-hritanniue as described by me^, all that is wanted 

 to complete the comparison being an account of the actual history of the organ in 

 Hemimerus in order to demonstrate its relation to the normal embryonic membranes 

 of the insect. 



The other fact which it is my fortune to bring forward in support of the suggestion 

 that the trophic vesicle here referred to is a formation of primary- or phylogenetic 

 significance, is due to the recent observations of M. Bouvier of Paris^. In a species of 

 the South Afi-ican genus Peripatopsis, namely, P. sedgwicki Purcell, M. Bouvier describes 

 a blastodermic vesicle with nuchal insertion as in Paraperipatus. The vesicle attains 

 relatively enormous dimensions, measuiing as much as 5 mm. in length in the case of 

 an embryo of -3 mm. M. Bouvier is of opinion that the species in question is the 

 most primitive member of the genus Peripatopsis and that the other species of this genus, 

 <vs regards then- development, are derived from it by atrophy of the vesicle accompanied 

 by greater simultaneity in the growth of the embryos. 



' The expression "great systematical importance" may be interpreted in various ways, but, for my part, 

 ] prefer to take it as signifying great phylogenetic importance. 



- Willey, A., "The anatomy and development of Peripatu.^ novae-britaiviiae," Zool. Results, Part i. 1898. 



•' Bouvitr, E. L., " Observations sur le developpement des Onychophores," C. R. Acini. Paris, tome 131, 

 p. 6.52, 1900. JI. Bouvier has again returned to this question (" Sur la reproduction et le developpement du 

 Pi-ripalopsis blainvillei," op. cit., tome 133, p. 518, 1901) in connection with the Chilian species whielk affords 

 a transition from the Andicoloas to the South African forms. He finds that the genus Peripatopsis presents 

 three modes of development: — 1. avec un oeuf tr^s petit et sans annexe embryonnaire (P. bluinvillei) ; 

 2. avec un ceuf assez volumineux et [avec] vesicule nuquale {P. sedgwicki) ; 8. avec un oeuf assez volumineux 

 et sans annexe embryonnaire (tous les autres Peripatopsis). In the second category 1 have placed the word 

 "avec" in square brackets, because, in the original, the word "sans" is inserted by an olivious typo- 

 graphical error. 



That all these deductions cannot be accepted without discussion goes without saying, but fortunately the 

 issue is fairly clear and an important presentation of the opposite view has quite recently been contributed 

 by Professor Arthur Dendy (" On the oviparous species of Onychophora," Quart. •/. .Micr. Sc, Vol. Li, 1902, 

 pp. 363—415, Pis. 19—22). Dendy thinks that the oviparity of certain Australian species which lay large 

 yolk-laden eggs is primitive, and adduces in support of this contention the consideration that the chorion 

 which surrounds the intra-uterine embryo in the viviparous species of Peripatiis may be regarded as a vestigial 

 structure inherited from oviparous ancestors in which a chorionic membrane acted as a protection to the 

 deposited egg during the early stages of development. It does not follow however that the eggs were primitively 

 overloaded with yolk, since most so-called alecithal eggs are also protected by a chorionic or vitelline membrane. 



