224 M, C. Meresclikowsky on new Species 



development of some species of Hydroids and Medusas, 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 hitentar.u- 

 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 Pohjxenia 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 Medusse 

 also show that at the commencement there appear only 

 two tentacles, and afterwards gradually two at a time are 

 added, as for instance in : — Oceania longuida, Ag. {Camjjanu- 

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

 nuluj Esch. ; Staurophora laciniata^ Ag. ; Stomotoca atra^ 

 Ag. ; Campanalina acuminata. Aid. ; different species of the 

 genus Perigonimus, the tentacles of which do not accumulate ; 

 also in th.Q, yEginopsis mediterranea^Zanclea implexa, Saphenia 

 halearica, S. hitentaculata, S. diadema, Oceania diadema^ 

 Octochila hitentaculata. Finally, from a number of facts 

 mentioned by Ehrenberg and Brandt, it is seen that the 

 departures from the normal number often present such num- 

 bers as are the product 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, which are not divisible by 

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

 carnea, which has 4, 6, 8, 10, and 12 tentacles, as is very clearly 

 shown 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 AUman, is 

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

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

 all these facts, to which I shall allude moi-e particularly 

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

 the number Avhich 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 Medusas (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 

 morphologrcal types. 



