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form only of A. pellucidum (Leidy), is that mixed colonies of these 

 two ascidians, such as those shown in the photographs, Plate 3, 

 in which a part of each colony has the appearance characteristic 

 of A. pellucidum, the remaining part, or parts, the appearance 

 characteristic of A. constellatum, are very frequently taken in the 

 dredge from the sandy and rocky bottoms of Vineyard Sound. 

 Van Name states, (1910, p. 404), ''This species [Amaroucium 

 pellucidum] exists in two very dissimilar forms, which have been 

 considered distinct species (the typical A. pellucidum, and A. con- 

 stellatum Verrill), but which are in reality not even true subspecies, 

 as is shown by some colonies which in one part have the typical 

 pellucidum characters, while in the remainder of the colony the 

 constellatum characters are equally well developed. There are 

 also specimens in which the whole colony has characters inter- 

 mediate between the two." " Where the coating of sand is abraded 

 or wanting, the test is seen to be translucent and gelatinous. In 

 such cases, there is a tendency of the lobules to be more or less 

 fused or united, and the specimen then approaches the form 

 stellatum ... in its characters" {ibid., p. 405). "Amaroucium 

 pellucidum develops into the typical sand-incrusted form on a 

 sandy bottom only. Where it grows on rocks or piles of wharves, 

 the constellatum form develops" (ibid., p. 348). 



Having found that typical A. constellatum colonies liberate 

 tadpole larvae that are strikingly different from those set free by 

 typical A. pellucidum colonies, careful dissections of the two types 

 of lobules present in the mixed colonies were made and, in every 

 case, typical constellatum tadpole larvae (Fig. 1, B), were found 

 in the constellatum lobules even in cases in which a single lobule 

 only, surrounded by hundreds of pellucidum lobules, was present; 

 and typical pellucidum tadpole larvae (Fig. 1, A), were invariably 

 found in pellucidum lobules. In no case were tadpoles of inter- 

 mediate characters found and, in this connection, it may be stated 

 that colonies which had characters intermediate between the two 

 species, such as are referred to by Van Name, (1910, p. 404), 

 have not come to my attention although hundreds of colonies 

 of both species have been handled each season for several years. 

 In practically all colonies composed of both pellucidum and con- 

 stellatum lobules, the pellucidum type predominates, indicating 

 that the pellucidum colony is the first to become established and 

 that it forms an object to which constellatum tadpole larvae sub- 

 sequently find place for attachment. In the dissection of mixed 



