ZOOLOGY AND BOTANY^, MICROSCOPY, ETC. 377 



thirteen varieties are considered, and some of their characters noted. 

 Triodopsis Sanhurni, T. Harfordiana, and T. Hemphilli, are new species. 

 In dealing with the species of the Pacific province, those from the extreme 

 northern region are not included, as they more properly belong to the fauna 

 of Asia. 



Molluscoida. 

 a. Tunicata. 



Colonial Vascular System of Tunicata.* — M. F. Lahille denies that 

 the colonial Tunicata generally have a common vascular system, and 

 asserted that this only is rarely present. The genera that have a colonial 

 plexus are those in which there is a basal stolonial blastogenesis, such as 

 Perophora, ClavuUna, some of the Cionidse, and some of their allies. What, 

 in other Tunicates, has been taken for such a plexus, has really a very 

 different significance ; in the Diplosomidse, Didemnidee, and Leptoclinidae, 

 there are muscular cones, which have a fixing function, and as they may be 

 very long and underlie the substance of the tunic, they have been mistaken 

 by M. Giard for vessels. In the Aplididse there is not even an appearance 

 of a colonial plexus; in the Botryllidse the anastomoses of the vascular 

 appendages only appear after blastogenesis. As most of the Synascidians 

 are merely aggregations, they are only separated from the Monascidians by 

 their blastogenetic origin, and as the entirely blastogenetic origin of the 

 cormus and the general presence of a colonial vascular plexus has been 

 shown not to obtain, M. Lahille thinks that there is no longer any reason 

 for separating these two orders of Tunicates. 



New Organ of Respiration in Tunicata.f — Prof. W. A. Herdman gives 

 an account of the structure and distribution of blood-cavities in the test of 

 various Tunicates ; the disposition and anatomical characters in the different 

 regions and layers of the test lead him to think that in most Ascidians these 

 tubes exercise more or less perfectly a respiratory function ; further evidence 

 is afforded by the relation which exists in many groups between this system 

 and the branchial sac or chief organ of respiration. When the sac is large 

 and highly developed, the vessels in the test are few and small, but when 

 the branchial sac is small, simple, and apparently inefficient, the vessels in 

 the test are numerous, of large size, and disposed in such a manner as to 

 suggest at once that they are concerned in the aeration of the blood. 



'Challenger' Tunicata. f — Prof. W. A. Herdman reports on the com- 

 pound Ascidians collected by the ' Challenger.' This, one of the most 

 difficult of all groups of animals, was represented by 25 genera and 

 102 species ; ten of the former and 88 of the latter are regarded as new. 

 The forms are chiefly littoral in habitat, only seven extending to a depth 

 of 1000 fathoms ; one of the most remarkable is Phenyngodidyon mirabile, 

 which was taken from a depth of 1600 fathoms. The compound Ascidians 

 are regarded by the author as having had a polyphyletic origin among the 

 simple forms. 



13. Polyzoa. 



Critical Notes on Polyzoa.§ — The Eev. T. Hincks commences by 

 discussing the characters of the family Adeoneae, with especial reference to 

 the " somewhat heterogeneous company " included in it by the late Mr. 



* Comptes Eendus, civ. (1887) pp. 239-42. 



t Proc. Lit. and Philos. Soc. Liverpool, xxxis. (1885) pp. 39-46 (1 pi.). 

 t Reports of the Voyage of H.M.S. 'Challenger,' xxxviii. (1886) pp. 432 (49 pis.). 

 § Ann. and Mag. Nat. Hist., xix. (1887) pp. 150-64. 

 1887. 2 



