8 



KR. BONNEVIE 



[REP. OF THE "MICHAEL SARS" NORTH 



to renewed examination, and then by the exact methods 

 of comparative anatomy attempt to formulate a series of 

 characters which shall be of real systematic value. 



Tesch (1906) has made a good move in this direc- 

 tion by drawing attention to the shape of the eyes and 

 nucleus as a point of significance for the distinction of 

 species; he also mentions the extension of the mus- 

 culature on the under side of the proboscis. Upon 

 these three characters he established the two subgenera: 

 1. Pterotrachea s. s. with cylindrical eyes, the retina of 

 which is scarcely broader than the distal part, with a 

 spindleshaped, long and narrow, nucleus, and with the 

 cross muscles of the proboscis covering its whole ventral 

 side; and 2. Euryopsis including those species with 

 broad eyes, the right and left sides of which diverge 

 greatly towards the base, with a short and swollen, 

 pear-shaped nucleus, and with a muscle plate covering 

 both the ventral and lateral sides of the proboscis, though 

 only through half its lenght. 



A distinction between these two subgenera will, 

 according to Tesch, prove easy enough, but characters 

 distinguishing the species are still wanting. And indeed, 

 his material seems to justify this view, for its subdivision 

 into the subgenera above mentioned is not difficult, while 

 at the same time six new species described by Tesch, 

 from the "Siboga" Expedition are characterized by only 

 relative marks, 1 ) which will not secure the recognition of 

 one species if a comparison with the others is excluded. 

 The size and development of the sexual organs, penis 

 and sucker, are by Tesch repeatedly used as specific 

 marks, although no information is given as to whether 

 the individuals had reached sexual maturity. 



I have thoroughly examined the specimens of 

 Pterotrachea from the "Michael Sars" Expedition, in 

 order to find, if possible, some features which might be 

 considered characters of real specific value, i. e. constant 

 in all the individuals of one species, but varying from 

 one species to another. 



The first result of my investigation is that I cannot 

 accept the two subgenera proposed by Tesch, based 

 upon differences in the eyes and nucleus and in the 

 musculature of the proboscis. 



') Thus P. challenged, is characterized (p. 85) "durch die 

 kurze, gedrungene Gestalt des Schwanzes, und weiter durch die be- 

 trachtliche Entwickelung des Saugnapfes und des Penis," - P. inter- 

 media, n. sp. (p. 86), erstens durch den langeren und niedrigeren 

 Schwanz, dann audi durch den kleineren und schwacheren Saugnapf". 

 — P. microptera, n. sp., finally is characterized by (p. 87), die relativ 

 kleine Flosse, welche nie die Grosse wie bei den vorhergehenden 

 Formen erreicht. "Bei den Mannchen kommt als ganz besonderes 

 Merkmal noch der auszerordentlich winzige Saugnapf hinzu, der kaum 

 sichtbar ist". 



I quite agree with Tesch that eyes and nucleus 

 represent very important systematic characters, and that 

 there is a conspicuous parallelism between these organs 

 in so far as relatively long cylindrical eyes are found in 

 species which have also a long and slender nucleus, 

 while broad-based eyes are met with in animals whose 

 nucleus is also broad and short. As already mentioned 

 by Gewerzhagen (1914), these two types do not however, 

 represent distinct groups in which the species of Ptero- 

 trachea may easily be distributed; they are only the 

 initial and final steps of an evolution within the whole 

 genus in a direction from the broad-based eyes and 

 nearly spherical nucleus of Cardiapoda to long cylindrical 

 eyes and a spindle-shaped nucleus. — A few steps of 

 this evolution is illustrated in textfig. A, showing eyes 

 and nuclei of five different species, or varieties, from the 

 material at my disposal. 



The third feature mentioned by Tesch, the proboscis 

 musculature, will scarcely prove a character of syste- 

 matic value, at least not of practical value in the deter- 

 mination of species or subgenera. For the fact is that 

 the appearance of this musculature differs very much 

 with its state of contraction, so much indeed that in 

 some individuals it can not be distinguished at all, while 

 in other individuals of the same species, in which the 

 cross muscle fibres are contracted, the plate is more or 

 less conspicuous. 



For these reasons I cannot regard the subgenera of 

 Tesch as expressions of the natural relations between the 

 species of Pterotrachea, and therefore I shall make no 

 use of them in my descriptions. A thorough examination 

 of the material at my hand has however, proved the 

 existence of a series of specific characters which, in the 

 present state of our knowledge, seem quite distinct and 

 unconnected by transitions. 



Such characters are: 



1) The shape of the eyes: whether they be cylindrical 

 or broadbased, and the relation between their width 

 and height. 



2) The shape of the nucleus: the proportion between 

 its width and heighth and between the latter and 

 that of the whole body. 



3) The cutis: a. Whether it is equally thick all over 



the body, or with a distinct shield-like swel- 

 ling at certain parts of the body. 



b. Whether it is smooth or provided with spots, 

 or tubercles, or both, and the arrangement of 

 such structures. 



c. The existence of cuti cul arspin es on the 

 forehead, in front of the eyes, in both sexes, or 

 only in one. 



