642 SUMMARY OF CURRENT RESEARCHES RELATINd TO 



hepatopancreas and alimentary canal consists throughout of well-marked 

 cubical cells and shows no specialization in any particular region. 



The nervous system consists of a minute supra-oesophageal mass of 

 transverse nerve- fibres devoid of nerve-cells- — a curious result of the 

 degraded habit of life — of two circumoesophageal commissures with 

 nerve-cells, aud of a comparatively thick ventral cord well supplied with 

 cells. No eyes or other sense-organs were recognizable. The animal 

 is hermaphrodite, and Dr. Fowler was able to make some observations 

 on the course of spermatogenesis. 



Petrarca is much more degraded than Laura ; no head region is dis- 

 tinctly marked off as such, only one pair of mouth appendages is recog- 

 nizable, the thoracic appendages are much simpler in character, the 

 abdominal region has almost disappeared, and segmentation occurs only 

 in the posterior region of the body. Both genera, however, as well as 

 Synagoga, belong to the Ascothoracida. 



The author discusses the views as to the relationship of the various 

 groups of the Entomostraca, and presents his own in the tabular form as 

 given on preceding page. 



Vermes. 

 a. Annelida. 



Formation of Stolons in Syllidians.* — M. G. Pruvot discusses sepa- 

 rately the formation of stolons in Syllidse and Autolytidae. In all cases 

 the stolons are produced by fission, which carries off a certain number of 

 indifferent preformed segments. The first phenomenon is the accentua- 

 tion of the groove which separates two consecutive segments ; this causes 

 the upper and lower trunks to become morphologically distinct from 

 one another ; the first then regenerates its caudal extremity, and the 

 second reforms its cephalic extremity by a process which is exactly com- 

 parable to that which happens when a real section is made between them. 



Natural History of Annelids.f — M. L. Yaillant has published what 

 may be regarded as a continuation of the well-known work of Quatre- 

 fages. In the first part, which alone is yet published, he deals with 

 the Lumbricid^, Lumbriculidae, and Enchytrseidaa on the methods of 

 Quatrefages' work. Considering the large numbers of species described 

 during the last three years, it seems a pity the work is not up to date. 



Phymosoma varians.|— Mr. A. E. Shipley has investigated the 

 anatomy of this West Indian Gephyrean. The head has a crovni of 

 tentacles, of which there are usually eighteen, arranged in a horse-shoe- 

 shaped lophophore, which is dorsal to the mouth. The mouth is 

 crescentiform. The cavity which represents the pre-oral lobe has a 

 peculiarly pigmented, curiously wrinkled epithelium ; this is continuous 

 with the brain, and from it two sensory pits descend into that organ. 

 At the posterior end of the introvert immediately behind the head a thin 

 but very extensible collar is attached ; the anterior end of this collar is 

 free, and when the introvert is inverted, it completely covers the head. 

 The ectoderm, except in the most anterior region, is one cell thick; it 

 is curiously vaulted and leaves irregularly scattered spaces between it 

 and the outside of the circular muscles, in which a nutritive fluid pro- 

 bably circulates. 



* Comptes Eendus, cviii. (1889) pp. 1310-3. 



t 'Histoire naturelle des Aunules maiins et d'eau douce/ iii., lere partie, 8vo, 

 Paris, 1889, 340 pp. J Troc. Roy. Soc. Lond., xlvi. (1889) pp. 122-6. 



