224 M. C. Meresclikowskj on new Species 



development of some species of Hydroids and Medusae, from 

 which it is seen that among the Hydroids, for instance, Clava- 

 tella prolifera^ which has in its normal state six tentacles, in its 

 youth has only two ; the same with Perigonimus hitentacu- 

 latus, which perhaps is an embryonic state of another hydroid; 

 to these belong also Perigonimus quadritentaculatus (which 

 has two more tentacles developed), Acharadria larynx, 

 and the Medusa Poli/xenia leucostyla (the tentacles of which, 

 as observed by MetchnikofF, make their appearance at first 

 two in number, and afterwards increase by twos) . A number 

 of facts in the history of the development of the Medusas 

 also show that at the commencement tliere appear only 

 two tentacles, and afterwards gradually two at a time are 

 added, as for instance in : — Oceania longuida, Ag. [Campanu- 

 lina, V. Ben.) ; Lafoea calcarafa, Ag. j Melicertum campa- 

 nula^ Esch. I Staurophora laciaiata^ Ag. ; Stomotoca atra, 

 Ag. ; Canipanulina acuminata^ Aid. ; diffei'cnt species of the 

 genus Perigonimus, the tentacles of which do not accumulate ; 

 also in the ^ginopsis mediterranea^Zanclea implexa, Saphenia 

 balearica, S. bitentaculata, S. diademOj Oceania diadema, 

 Octochila bitentaculata. Finally, from a number of facts 

 mentioned by Ehrenberg and Brandt, it is seen that the 

 departures from the normal number often present sucli num- 

 bers as are the })roduct of 2 multiplied by 5, 7, 9, 15, &c. 

 (10, 14, 18, 30, 170). Most frequently after the number 4 

 we meet with the number 6, which is evidently 2x3; 

 whereas the numbers 3, 7, 17, whicli are not divisible by 

 2, are seldom met with. The same is seen in Podocoryne 

 cai-nea, which has 4, 6, 8, 10, and 12 tentacles, as is very clearly 

 shoAvn in the drawings of Hincks. Cladonema radiatum, 

 which is described by all authors as having ten radiating canals 

 (2 X 5), in England, according to the researches of Allman, is 

 always found with eight (2 x 4) canals. Clavatella prolifera 

 often has eight instead of six tentacles (in the hydranth). From 

 all these facts, to which I shall allude more particularly 

 another time, it follows that the fundamental number (that is, 

 the number which first appeared, and through the repetition of 

 which were produced all the numbers which we now meet) of 

 the Hydroids as well as of other Medusee (and all Coelenterata, 

 in opposition to the Echinodermata, in which five is the num- 

 ber) is 2 ; and if we accept as real the biogenetical law, it 

 follows that the forefathers of the present Hydroids had only 

 two tentacles, and that, in consequence of the repeating of the 

 number two 2, 3, 4, 5 times and so on, there appeared other 

 morphological types. 



