196 SUMMARY OF CURRENT RESEARCHES RELATIITG TO 



Gemmation in Didemnidae and Botryllidae.* — A. Delia Valle 

 finds that the body of each animal, when adult, consists as in the 

 true Enterocoelia, of two epithelial sacs, ectodermal and endodermal, 

 which are separated by a cavity occupied by a true enterocoele, a sac 

 derived from the intestine ; this cavity communicates with the exterior 

 directly by the cloacal orifice, and indirectly by the branchial clefts. 



All the organs which are not directly derived from the true 

 endoderm (sexual organs, heart, and muscular fibres) arise between 

 the ectoderm and the parietal wall of the coelomic sac. 



As to the question raised by Prof. Huxley as to whether the Asci- 

 dians are true Enterocoelia, we have to note that the question is based 

 on the belief of Kowalewsky and other observers that the atrial orifices 

 and the atrial sacs themselves are formed from the ectoderm. The 

 author, however, finds that after the formation of the branchio-intes- 

 tinal sac two estroflexions arise in its lower part ; these grow rapidly 

 and soon cover part of the median sac ; this last is prolonged down- 

 wards to form the intestine, which becomes folded against one of the 

 extroflexions, while the lateral sacs approach the ectoderm. Where 

 they do so the ectoderm forms an introflexion, and, the opposed cseca 

 meeting and vmiting, we have the endoderm communicating with the 

 exterior by two orifices ; these, later on, unite and form the permanent 

 cloacal orifice. Dealing w^ith the statement of E. van Beneden that 

 the enteroc<Tele of the larva disappears completely, the author 

 points out that this view is not only contradicted by the evidence 

 afibrded by a transverse section but also by an inspection of a living 

 Perophora, where the blood-corpuscles in the branchial sac may be 

 seen moving between two membranes. Contrary to the views of 

 " Jolin " (? Julin) the author agrees with a number of other ob- 

 servers in regarding the body-cavity of AmpMoxus as exactly com- 

 parable to the peribranchial cavity of Ascidians. 



In the Didemnidae gemmation is a cause of rejuvenescence, or of 

 the formation of new individuals ; either of them are always due to 

 the connection of two buds, which may be " brothers," or " mother " 

 and " daughter," or " grandmother " and " granddaughter." During 

 their period of adhesion the buds are the cause of polymorphism. In 

 the Botryllidfe one bud is sufficient for the production of a new 

 individual, and this is formed by an extroflexion of the parietal wall 

 of the peritoneum of the parent which gives rise to a similar extro- 

 flexion of the ectoderm ; as a rule there is but a single bud on either 

 side ; as soon as the peritoneal sacs are developed, the new buds are 

 ordinarily provided with generative organs ; in some cases, however, a 

 whole colony may be seen to be wdthout ova. 



Anatomy and Histology of Ciona intestinalis.f — In this her- 

 mai)hrodite Ascidian L. Eoule states the testis and ovary to be 

 distinct from each other ; their activity lasts throughout the year. 

 The testis consists of an aggregation of tubes inclosed by the 

 connective tissue of the wall of the intestine, i. e. of the curvature 



* Arch. Ital. Biol., ii. (1882) pp. 50-72 (3 pis.). 



t Comptes Kendus, xciv. (1882) pp. 1652-5, 1726-9. 



