630 SUMMARY OF CURRENT RESEARCHES RELATING TO 



albidum, A. duplex (sp. n.), and Pherusa tuhulosa. The ova of the first 

 of these escape into the perivisceral cavity, whence they are severally 

 projected to the exterior by the so-called intertentacnlar organ, the 

 function of which has been so much discussed. In A. duplex the phe- 

 nomena are more complicated and more interesting. When the sexual 

 elements are about to be developed, the zooecium is occupied by a 

 polypide, without any intertentacular organ, and a cellular mass, which 

 is destined to form the spermatozoa, appears by the wall of the gastric 

 caecum. Towards the aboral extremity of the same zooecium there is 

 formed a second polypide, on the funiculus of which young ova appear. 

 The older polypide appears to be the male, the younger the female. 

 The former soon begins to degenerate, and leaves the brown body and 

 the mass of spermatozoa ; the female polypide is now seen to be provided 

 with an intertentacular organ, which conveys the ova to an invaginated 

 sheath, where development is effected as in a marsupium. Pherusa, like 

 Memhranipora and Flustrella, has a bivalved larva. 



Arthropoda. 



Ancestors of Myriopods and Insects.* — Prof. B, Grassi has an 

 elaborate essay on the comparative anatomy of the Thysanura, together 

 with some general considerations on the organization of Insects. The 

 external skeleton and the segments are first dealt with ; there are three 

 thoracic segments, and ten abdominal ; those authors are incorrect who 

 regard the anal valves as representing a segment ; like the Thysanura, 

 the embryos of higher insects, e. g. the bee, have ten abdominal segments. 

 The author does not think that the epicranial suture is of any assistance 

 in determining the number of cephalic segments. 



The disposition of the muscles does not afford any support to the view 

 that the Thysanura have lost wings which they once had ; on the other 

 hand, we may say that just as they are provided with lateral prolonga- 

 tions which might well be developed into wings or gills, so are they in 

 the same way provided with muscles which would enter into the service 

 of such organs. Although the musculature of these low insects is divided 

 into dorsal and ventral portions and into lateral areas it has no intimate 

 relations with that of Peripatus. 



The respiratory system is treated of in the third section. The most 

 primitive arrangement seems to be found in Japyx solifugus, where 

 there are eleven pairs of stigmata, four thoracic, and seven abdominal. 

 Campodea has only three pairs of thoracic stigmata, the third, as well as 

 the last seven of Japyx solifugus, being wanting. In J. Isahellse there 

 are two thoracic and seven abdominal pairs, and the same is the case 

 with Machilis. The Lepismidse have probably three thoracic and seven 

 abdominal. The fact that J. solifugus has four pairs of thoracic stigmata 

 points to the conclusion that the original position of the thoracic stigmata 

 was not segmental. The conditions found in the Lepismidse are retained 

 by the Blattidse, and by the Orthoptera generally, and they are also 

 reproduced in the embryo of the Bee. The author's observations tend 

 to modify considerably the fundamental conclusions of Palmen — for 

 example, we must accept Gerstaecker's view that a large number of 

 Insects have still three pairs of stigmata and not two ; there is a direct 

 passage between the conditions which obtain in the Thysanura and in 



* Atti E. Accad. Lincei.— Mem., iv. (1887) pp. 543-606 (5 pie.). Arch. Ital. 

 Biol., xi, (1889) pp. l-ll, 291-337, 389-419 (.5 pis.). 



