ZOOLOGY AND BOTANY, MICEOSCOPY, ETC. 835 



on each side of the anterior end of the embryo of a cavity which 

 divides the layer into two, one of which is attached to the ecto-, the 

 other to the endoderm ; shortly after, a similar pair of cavities appear 

 behind the first, and so on backwards — the earliest condition of the 

 body-cavity. The embryo lengthens backwards, and becomes much 

 folded on itself. The head-segment is the largest, and consists of two 

 globular halves. The primary mouth and anus appear to be replaced 

 by later developments. The segmental appendages appear as pairs of 

 arched processes ; the first pair, the mandibles, are surrounded by a 

 number of secondary papillae, and are withdrawn into a large buccal 

 cavity ; the second form the excretory papillae of the slime-glands ; 

 the antennae present dorsal processes of the two cavities in the head. 

 After the total number of segments has been formed, the nervous 

 system arises as a series of paired ventral thickenings of the ecto- 

 derm, soon detaching themselves, and extending along the body from 

 the brain, which has arisen in a similar way. 



After the formation of an oesophagus, the mode of nutrition by the 

 dorsal pedicle, or " umbilical cord," and placenta seems to be replaced 

 by prehension of uterine epithelium by the mouth. 



As to the relations of the primitive and adult mouth and anus and 

 the origin of the mesoderm, von Kennel will be seen to be widely at 

 variance with Messrs. Moseley and Sedgwick's interpretation of Prof. 

 Balfour's preparations and drawings, which, however, do not relate to 

 the earliest stages of the development, and which it may be men- 

 tioned were made on a different species. 



y. Arachnida. 



Pentastoma Lari.* — P. Megnin describes a new and remarkable 

 Pentastomum found in the air-sacs of Larus glaucus. About six cen- 

 timetres long and one broad, it has at first sight the appearance of a 

 Trematode, but a microscopic examination reveals the presence of two 

 pairs of symmetrically placed hooks at the anterior end. The new 

 species is remarkable for the attenuated form of the anterior extremity, 

 and the absence of any external annulation. At the front end there 

 are two tubercles which look like aborted antenn®, and below there 

 is an indication of a kind of segment. 



On what may be regarded as the second ring there is a pair of 

 small appendages, formed of two joints, which call to mind the cha- 

 racters of larval Pentastomes. The characters of this new species 

 resemble greatly those of the Lernaeidae, and especially of the 

 Chondracanthidae, and seem to M. Megnin to raise the question of the 

 systematic affinities of these parasites. If the resemblance to the 

 Lernaeidas is a real one, the Pentastomidfe should be ranged rather 

 with the Crustacea than with the Arachnida. 



d. Crustacea. 



Eesearches on tlie Isopoda.f — L. Huet, among the important 

 additions which he has made to our knowledge of these Crustacea, has 



* Bull. Soc. Zool. France, viii. (1883) pp. 153-6 (1 pi.). 

 t .Journ. Anat. et Physiol., xix. (1883) pp. 241-376 (4 pis.). 



