ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 593 



may be defined as an advance of the morphological on the physio- 

 logical state of the embryo. 



Here, as elsewhere, the solid mesoderm developed around the 

 prostoma appears before the cavitary mesoderm ; the first gives rise to 

 the skeletal and muscular organs, the other to the blood-vascular 

 system and serous membranes proper. The striated muscle is not 

 characteristic of either of these parts of the mesoderm, for it may, in 

 the same individual, be found in the tail of the larva, and in the 

 muscular layer of the heart. 



Anatomy of Pyrosoma* — L. Joliet, in a further note, observes that 

 the four primitive individuals in P. gigardeum are to be found not at 

 the closed but at the open extremity of the colony, and he explains 

 how they are " incessantly pushed away " from the closed end by the 

 development of their progeny. The nervous system of the primitive 

 ascidiozooids has its two lateral posterior nerves terminating at two 

 muscular cords, but in ordinary individuals there is only one of these 

 cords, which receives both nerves, and is the morphological represen- 

 tative of both cords. The bundles forming the colonial muscular 

 system are reported to be formed from modified cells of the '" common 

 transparent substance." The author cannot assent to the doctrine that 

 the elasoblast represents the tail of the ApjjendicularicE, and he looks 

 upon it as affording a store of nutriment for the young. To exactly 

 compare Pyrosoma with Salpa, we must take the cyathozooid and the 

 agamic Salpa as equivalent terms. 



Australian Bryozoa.f — Mr. E. H. MacGillivray forms a new 

 genus Diplopora, for a species which he considers was described by 

 Hutton as Memhranipora cincta. The cells are divided into two 

 parts, the posterior portion being much elevated, and there is a 

 narrow transverse portion a little distance behind the mouth, and in 

 front of the elevated part, deficient in calcareous matter and entirely 

 membranous. 



The other genus is Densipora, considered to belong to the family 

 Diastoporidffi, and is represented by one species called Densipiora 

 corrugata, and considered to be described for the first time, but it has 

 already been cited as living in Australia, and was considered to be 

 Heteropora cervicornis of D'Orb. The description of the full-grown 

 individuals seems to leave no doubt as to the relationship to Heteropiora ; 

 but the young specimens, the author says, show Diastoporidan charac- 

 ters, and therefore he places it under that family. This observation 

 is of great interest now that attention is being drawn to the class 

 position of Heteropora, and living and young specimens have not 

 been available for those who have entered upon the discussion, but if 

 the present interpretation is correct it must entirely support the 

 Bryozoan affinity of Heteropjora. As this is very important, we give 

 the description of the young specimen said to show its Diastoporidan 

 character. " The smallest specimen I have is about one-twentieth of 

 an inch in diameter, is discoid, of considerable thickness in the 



* Comptes Eendus, xcii. (ISSl) pp. 1013-14. 

 t Proc. R. Soc. Victoria (not yet received}. 



