MARINE ZOOLOGY 



Ascidiella aspersa, O. F. MuUer (cont.) j^sdriia productii,V{3.ncoQk. In 1901 this was fairly 



white grapes. Lower down large and ex- abundant in the lower part of the Orwell, 



cellent specimens were obtained. Fairly often much attached along its side to dead 



common in the lower parts of all the shells and other objects 



estuaries. The great number of the larvae Ciona intfstina/is, Linn. In 1890 unusually good 



in the water is shown by the fact that we specimens could be obtained by dredging at 



have sometimes cleaned off the bottom of the ' the Rocks ' in the Deben above Ramsholr, 



yacht so many young individuals mainly of but not in later years. It occurs in most of 



this species that I estimated them at about the other estuaries and in the open water 



100,000 which must have attached them- outside, but is not common, and often very 



selves within no considerable period of time dirty 



— virginea, O. F. MilUer. Compared with the Clavelina lepad'iformis, O. F. Milller. I do not 



above-named species this is rare remember finding this actually in Suffolk, 



Ascidia pkbein. Alder. Found in the lower part but cannot believe it is absent, since it is 



of the Stour, but is not common fairly common within a few miles in Essex 



COMPOUND ASCIDIANS 



Some of these are conspicuous and attractive objects, and some very obscure and of little 

 interest, except for microscopic observation. 



In the later months of summer the banks of the Orwell near Pinmili at extreme low 

 water are an excellent locality for the study of Botrylli., but this is made somewhat difficult by 

 the fact that they so soon die and decompose in hot weather, even when kept in a large 

 aquarium, so that it is almost impossible to compare living specimens collected on different 

 days. The individual colonies differ very greatly in colour from dark blue and dark grey to 

 flesh colour and yellow, and the difficulty is to make out how far this is due to difference ir 

 species or to extreme variation. This fact is fully recognized by Professor Herdman in his 

 paper on the classification of the Tunicata in the Journal of the L'tnnean Society? 



After many trials I found that it was possible to preserve the specimens mounted in 

 Canada balsam, so that they could be compared in subsequent years with lower or higher 

 magnifying powers. The only important change is that the formalin used in the preparation 

 soon alters the blue pigment of some varieties into a brownish red one, similar to, if not 

 identical with, that which occurs naturally in the closely allied genus Botrylloides. On 

 examining these specimens it was soon seen that not only the well-preserved colour varies from 

 a more or less brown red to pale yellow, but there is much variation in its distribution, and a 

 very great difference in the general character of the individual animals. The difficulty, how- 

 ever, is that these differences are not those taken notice of in the published accounts of the 

 different species, so that, although it is easy to recognize what may be specific differences, it is 

 difficult to assign the proper names. It was soon seen that independent of colouring they could 

 be separated into three groups which differ so much that one feels constrained to look upon 

 them as species until a more extensive series of specimens furnishes connecting links. One of 

 these groups, however, shows great differences, and one must conclude that there is either a 

 single very variable species or else three or even four closely-related species, which differ mainly 

 in the extent and manner in which the colour is distributed. One of these possible species 

 seems to correspond with Botryllus sch/osseri, and another may be what has been called B. 

 polycyclus, but the difficulty of corroborating the observed structures with published descriptions 

 seems to show that much remains to be learned before anything more can be said than that, 

 though there may be several true species there is very great variation in some members of 

 the group, and it is difficult or impossible to say whether the characters are or are not of 

 specific value. 



Botrylloides rubrum, M. Edw. I have found a few specimens in the Orwell, but since the 



specimens on the pier at Harwich and in water has been muddy they have been 



the Orwell, but it is far from common inferior in colour 



— leachu,?>dLV. Previous to 1900 good specimens Didemnum ; Leptocl'mum ; Diplosoma. These occur 



could be dredged in the Orwell below Pin- in the Orwell, but the species have not 



mill, but after that they were inferior, been studied in a satisfactory manner 



mainly owing to the muddy state of the Appendicularia (Chamisso). Specimens of these 



water animals are common in the sievings of sea 



Polyclinum aurantium. I have dredged a few water along the coast 



' Aug. 1 891, xxiii, 606. 

 95 



