56 SUMMARY OF CURRENT RESEARCHES RELATING TO 



and of the embryonic membranes ; in the second the organs are laid 

 down, and in the third they arc developed. The postembryonal 

 development of the larva may be regarded as a fourth period, during 

 which the generative organs appear. 



This essay is not only of imj)ortauce on account of the author's 

 own investigations, but also from the way in which the accounts of 

 other workers at insect embryology are stated, compared, and 

 criticized. 



'y. Frototracheata. 



Development of Peripatus.* — J, von Kennel has published in 

 detail an account of his observations on the development of Peripatus 

 cdwardsi and of P. torquatus ; his preliminary notice was reported on 

 at such length f that it is now only necessary to direct attention to 

 his concluding general remarks. 



Like Balfour and Metschnikoff, he sees a great resemblance 

 between the young stages of Peripatus and other Arthropods; the 

 resemblances to the annelids are much less striking. The characters 

 of the cephalic segment arc discussed, and the " praioral portion " 

 stated to be nothing more than the median mesoderm-free portion of 

 the first and oldest segment of the body, which contains a small 

 enteric cfecal sac. It is true of Arthropods that the frontal lobes 

 are the oldest segment of the body or head. The mode of origin of 

 the ccelom is such that it cannot be said to be either a schizoccele or 

 an enterocoele ; and the author proposes to speak of it as a neutrocajle. 

 Especial imjiortance is attached to the amnion and the connected 

 umbilical cord, but it is to be borne in mind that these terms are 

 used in a physiological and not in a morphological sense. The 

 former is compai'ed with the embryonic investments of scorpions 

 and insects, and the question is raised as to whether the so-called 

 dorsal organ of various Crustacea is a comparable structure. Though 

 the present state of our knowledge is far from satisfactory, it appears 

 probable that all the investments of the egg of the Tracheata are 

 comiiarablc inter se, and, if so, the " amnion " and " umbilical cord " 

 of the West Indian species of Peripatus are to be brought into the 

 same category ; the latter are, too, clearly seen to have a close 

 resemblance to the dorsal organ of the Crustacea, and von Kennel 

 cannot doubt the homology of the parts found in Oniscus and 

 Peripatus respectively. 



The direct descent of Peripatus from annelid or annelid-like 

 ancestors can no longer be questioned, and the organs just mentioned 

 seem to the author to be the representatives of the trochosphcre. 



5. Arachuida. 



Structure of the Fore-gut of Arachnida.]: — J. MacLeod describes 

 the structure of the " anterior intestine " of the Arachuida, by which 

 he clearly means the part to which English morphologists are in the 

 habit of applying Prof. Lankester's name of stomoda^um. 



* Arbeit. Zool.-zoot. Inst. Wiiizburg, vii. (1884) pp. 95-229 (7 pis.)- 



■f See this Journal, iii. (1883j p. 833. 



X Bull. Acad. R. Belg., liii. (1884) pp. 377-91 (15 figs.). 



